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Board Rounds Prep for USMLE and COMLEX
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Board Rounds Prep for USMLE and COMLEX

作者: Ryan Gray
最近更新: 2020/5/13
A collaboration between the Medical School Headquarters and BoardVitals, Board Rounds for the USMLE ...

Recent Episodes

33: Thinking Through a Radiating Holosystolic Murmur

33: Thinking Through a Radiating Holosystolic Murmur

Session 33 This middle-aged male has hypertension and diabetes. Which cardiac abnormality is giving rise to his radiating, high-pitched, holosystolic murmur? We’re joined by Dr. Mike Natter from BoardVitals. Go check out his amazing artwork on Instagram @mike.natter. Listen to this podcast episode with the player above, or keep reading for the highlights and takeaway points. [02:30] Question of the Week A 58-year-old male is presenting for an evaluation of a heart murmur that was recently discovered at a work health fair. His past medical history is remarkable for hypertension and diabetes. He has a nice chest pain, palpitations, syncope, or dyspnea. Cardiac auscultation reveals a high-pitched, blowing, holocystolic murmur at the apex. It radiates toward the axilla. The murmur does not increase in intensity with inspiration. What is the most likely diagnosis? (A) Mitral stenosis (B) Ventricular septal defect (C) Tricuspid regurgitation (D) Aortic stenosis (E) Mitral regurgitation [Related episode: USMLE and COMLEX Prep: 60 y/o Male with a Murmur] [03:43] Definition of Terms Holosystolic means you hear the sound throughout systole. It's not going away at any point, increasing or decreasing. It's just going. The apex of the heart is the opposite of the base. It can be sometimes confusing for medical students because it's almost the opposite of what you look at when you're looking at the heart. So the apex of the heart is located at the bottom. It's the inferior part of the heart. [06:17] The Correct Answer and the Thought Process Behind It If it's holosystolic, it's the systole. The ventricles are contracting. So what we're hearing is blood flowing back. It's the regurgitation through either the tricuspid or the mitral valve. Typically, where you're hearing the sound is the blood coming at you. So I'm narrowing my choices here down to either (C) Tricuspid regurgitation or (E) Mitral regurgitation. Mike points out that it's a good test-taking strategy to narrow down your choices. In this case, the correct answer is E. You want to look at pitch, location, and timing. You can grade murmurs and where it radiates, etc. Based on what's going on, we're dealing with a regurgitating murmur.  The murmur of mitral regurgitation gives you this blowing holosystolic sound and radiating to the axilla. It's a pathognomonic mitral regurgitant's description. So anytime you hear that description, it's telling of a mitral regurgitant murmur. It's essential to memorize the patterns because once that's done, you'll get those points easy. [12:08] Understanding the Other Answer Choices Mitral stenosis is characterized by more turbulent flows. Blood is trying to push through something that's basically closed. With stenosis, imagine the blood is knocking at the door and you hear a very hard clunk, clunk, clunk. It's very different from a blowing murmur or regurgitant-type murmur which sounds like a "woosh, woosh, woosh." Ventricular septal defect (VSD) is a defect between the two ventricles. What happens here is that blood is going to go from high pressure to low pressure. It sounds like a train going over a bridge "chug, chug, chug." In this condition, you're going to have the blood going from the left ventricle into the right ventricle. You will hear that extra sound in the heart as well. You could hear this on the bicuspid area although it's also going to be a holosystolic murmur. In...

2019/10/23
21:12
31: A Lung Tumor With Popcorn-Like Calcifications

31: A Lung Tumor With Popcorn-Like Calcifications

Session 31 A 55-y/o heavy smoker is shown to have a peripheral, well-circumscribed mass with popcorn-like calcifications in the RUL. What is the lesion likely composed of? Dr. Karen Shackelford from BoardVitals joins us once again as we delve into another case to prepare you for your Step 1 or Level 1 exam. Save 15% off their QBank by using the coupon code BOARDROUNDS. BoardVitals has a powerful QBank with comprehensive explanation and rationales behind all of their questions. Get up-to-date board review questions. You can avail of their 3 or 6-month plan and ask a clinician. Ask one of the physicians behind all of the questions. Listen to this podcast episode with the player above, or keep reading for the highlights and takeaway points. [01:48] Question of the Week: A 55-year-old male with a 40-year history of smoking who undergoes a low-dose chest CT for lung cancer screening. Imaging results show a peripherally located, well-circumscribed 2-cm mass in his right upper lobe. It has a popcorn-like calcification. Which of the following describes the characteristics of this mass? (A) is composed predominantly of fattened cartilage (B) is composed of poorly differentiated neuroendocrine cells (C) is composed of significant glandular components (D) is caused by keratin production and intracellular desmosomes (E) is formed by caseating granuloma around the causative organism [03:00] Thought Process Behind the Correct Answer The correct answer here is Answer choice E refers to TB and this doesn't sound like TB as there are popcorn lesions with TB. Answer choice A would sound more or less of a benign tumor. B sounds like a malignant small cell lung cancer. C would make you think of adenocarcinoma. [03:00] Thought Process Answer choice A would sound more or less of a benign tumor. B sounds like a malignant small cell lung cancer. C would make you think of adenocarcinoma. Answer choice E refers to TB and this doesn't sound like TB as there are popcorn lesions with TB. The correct answer here is A. A well-circumscribed lung tumor with predominantly fattened cartilage is a hamartoma. A trick that helped me remember this back in medical school is that “popcorn isn’t bad.” It's the most common benign tumor of the lung. It usually contains connective tissue, fat, and cartilage. It's classically associated with popcorn-like calcifications on imaging. They are relatively large, well-demarcated and they rarely impinge on surrounding structures. For the management of pulmonary hamartoma, it would be more beneficial not to undergo surgery. The approach to those tumors is individualized unless it's diagnosed as a stable nodule. Karen stresses the importance of not overdiagnosing people. Once you figure out it's not causing any problems, you just leave it there. [06:08] Understanding the Other Answer Choices The poorly differentiated neuroendocrine cells is a small cell lung cancer. It's a really aggressive malignancy that is most common in smokers. They usually have irregular margins and has a really poor prognosis largely because it tends to metastasize. Significant glandular components are characteristic of adenocarcinoma. It's the most subtype of lung cancer. It has both solid and ground blast components on imaging. It's a pretty heterogenous-looking tumor. It's usually peripherally located. Keratin production and intracellular desmosomes are characteristic of squamous cell carcinoma. It's a common form of non-small cell lung cancer. It originates from epithelial cells along the airways. They're usually centrally located, often associated with the larger bronchi. Caseating granuloma is characteristic of pulmonary tuberculosis around the causative organism. It...

2019/9/11
09:05
29: What Do Neurotransmitters Have to Do With Amenorrhea?

29: What Do Neurotransmitters Have to Do With Amenorrhea?

Session 29 Which of these neurotransmitters is mostly likely causing this patient’s galactorrhea and secondary amenorrhea? Where is it coming from? Dr. Karen Shackelford from BoardVitals. When you're looking to prepare for your Step 1 or Level 1 board exams, check out how BoardVitals can help you. You can find all their amazing QBanks for Step1, Level 1, or even any of your SHELF exams. Use the coupon code BOARDROUNDS to save 15% off. Listen to this podcast episode with the player above, or keep reading for the highlights and takeaway points. [01:37] Question of the Week A 34-year-old woman presents with amenorrhea for six months (secondary amenorrhea). Her menstrual cycles have been regular until this episode. She has, most of her life, a period every 28 days with a menstrual period that lasted three days. Today, on exam, a white nipple discharge is noted. A test for urine hCG is negative. Which of the following neurotransmitters suppresses the release of the hormone responsible for her condition? (A) Dopamine (B) Insulin (C) Serotonin (D) Somatostatin (E) Vasopressin [Related episode: Why Is This Menstruating Patient So Sick?] [02:50] Thought Process Behind the Correct Answer The correct answer here is A. If you think about the treatment for prolactinoma, where prolactin is released from the anterior pituitary, bromocriptine and cabergoline are used to shrink the prolactinoma. They're both dopamine agonists. The patient's symptoms are suggestive of prolactinoma. It's not totally obvious though as there wasn't headaches or visual field issues mentioned. Nevertheless, prolactinoma is the most common of all pituitary adenomas. It's also the most common cause of galactorrhea. The clinical features include amenorrhea, galactorrhea, and infertility. The prolactin normally stimulates the mammary glands to produce milk and inhibits the secretion of gonadotropin-releasing hormone, which results in amenorrhea and infertility. With large tumors, like the compression of the optic chiasm that results in bitemporal hemianopsia. Dopamine is normally used to suppress and release the prolactin. When you're not breastfeeding after birth, this becomes an issue. [05:15] Understanding the Incorrect Answers Insulin is produced by the pancreas and it's necessary for the uptake and utilization of glucose. Serotonin agonist is available in several classes, used as antidepressants. They're used to treat migraines, but not for prolactinoma. Additionally, some antipsychotic agents interfere with prolactin. Somatostatin is a hormone secreted by the pancreas that inhibits secretion of insulin and glucagon. It reduces the activity to digest the system. It's not receptive to dopamine and not related to galactorrhea. Vasopressin is an antidiuretic hormone and it's not affected by dopamine agonist. [06:22] Key Takeaways The key concept is that prolactinoma is probably the most common type of pituitary tumor and is the most common cause of galactorrhea. The symptoms occur because prolactin stimulates the mammary glands and suppresses GnRH, causing amenorrhea and infertility. The dopamine agonist suppresses prolactin secretion and shrinks the prolactinoma. Links: BoardVitals (coupon code BOARDROUNDS to save 15% off)

2019/8/14
07:49
28: The Clinical Signs of Renal Allograft Rejection

28: The Clinical Signs of Renal Allograft Rejection

Session 28 A patient with a 2-month-old kidney transplant has elevated creatinine, fever, and tenderness at the graft region. What other finding is likely present? As always, we’re joined by Dr. Karen Shackelford of BoardVitals as we dig into today’s case to help give you a better understanding. Listen to this podcast episode with the player above, or keep reading for the highlights and takeaway points. [01:02] BoardVitals If you're preparing for your USMLE Step 1 or COMLEX Level 1, check out how BoardVitals can help you prepare for your exam. Use the promo code BOARDROUNDS to save 15% off their QBanks. They have the 3-month version with over 1,700 questions. Once you're in medical school, they also have QBanks for the SHELF exams. [02:24] Question of the Week The patient who has a history of kidney failure as a result of multicystic kidneys has an allograft kidney transplant. Two months later, she presents with fever, malaise, and tenderness in the graft region. Her lab work shows a rise in creatinine. What other finding is characteristic of her condition? (A) Hypotension (B) Decreased graft size on the ultrasound (C) Patchy mononuclear cell infiltrates without tubulitis (D) Urinary obstruction (E) Oliguria [03:20] Thought Process The correct answer is E. The oliguria is a frequent finding. She has fever, malaise, and graft tenderness. Some patients can actually be asymptomatic during acute renal transplant rejection. They usually have hypertension that's why answer choice A is wrong. The graft may actually be enlarged on ultrasound. Creatinine only rises when there's significant histologic damage. If the graft rejection progressed, there would be weakness and fibrosis. You would have a decreased graft size but not at this point. Patchy mononuclear cell infiltrates without tubulitis is a pathological description of something that occurs in patients who have a normal functional renal allopath. So the histopathological findings in patients with rejection may have findings of interstitial infiltration with mononuclear cells, sometimes eosinophils. And the tubular basement membrane will be disrupted by these infiltrating cells. This is tubulitis. Along with inch-small arteritis, it's considered the primary lesion of acute cellular rejection. Acute antibody-mediated rejection is characterized by vasculitis with neutrophils, anti-glomerular and peritubular capillaries fibrin, thrombi, or nephrosis. Then there's interstitial hemorrhage, the presence of CD4 and antibody-specific to the donor suggest an antibody-mediated reaction. In chronic allograft dysfunction, you will see peritubular basement membrane splitting and multi-layering of the basement membrane.  The antibody-mediated rejection is an albumin response that occurs as antigen-antibody complex fixes complement with the activation of multiple complement protein. C4D is the component of the normal complement pathway. When C4 is split into C4A and C4B, C4B is then converted to C4D. This binds covalently to the endothelial basement membrane and the collagen basement membrane. In a normal kidney, C4D can be found in the glomerular mesangium and at the vascular pole. But the excessive reduction of immune complex deposition disease results in accumulation in the glomerular capillaries. The CD4 deposition can be seen by monoclonal antibodies staining and fluorescent tissue immunofluorescence. Peritubular capillaries staining is useful in just renal allografts. In acute allogra rejection graft, they appear large. Urinary obstruction is not the mechanism of oliguria in patients with renal allograft rejection. [09:20] Definition of Acute...

2019/8/7
12:06
27: Peptides and Isolated Cardiac Amyloidosis

27: Peptides and Isolated Cardiac Amyloidosis

Session 27 A patient with a history of arrhythmia is found to have atrial amyloid deposition on autopsy. Do you know what peptide is associated with this finding? Dr. Karen Shackelford joins us for another round of interesting questions to help you ace your boards. If you haven’t yet, check out BoardVitals and use the promo code BOARDROUNDS to save 15% off. Listen to this podcast episode with the player above, or keep reading for the highlights and takeaway points. [02:14] Question of the Week The autopsy of the patient with a history of arrhythmia revealed amyloid deposition in the atria but no other amyloid was found in the ventricles. Which of the following peptides is associated with amyloid deposition in the atria? And what is that peptide's function? (A) Calcitonin and reduction of blood calcium concentration (B) Prolactin and gastric emptying (C) Acetylcholine and positive chronotropy to sinoatrial node (D) Immunoglobulin and cell-mediated immune response (E) Atrial natriuretic peptide and vasodilation [Related episode: Cardiac Electrophysiology—What is it?] [03:15] Thought Process Behind the Correct Answer The correct answer is E. An amyloid is a group of diverse extracellular proteins in variable amino acid sequences and they have common physical properties. Amyloid deposition and the extracellular deposition of the fibrils are composed of the subunit of varied serum proteins that form beta-pleated sheet configurations that lead to the histologic changes seen in amyloidosis. Isolated amyloidosis is found only in a single organ such as this cardiac amyloidosis. Alpha-atrial natriuretic peptide is responsible for deposition in this isolated cardiac amyloidosis. This is what's responsible for amyloid deposition in part. The incidence appears to be maybe part of the normal process of aging. In one autopsy series, 86% of the patients between the age of 81 and 90 had isolated atrial amyloidosis. It may lead to heart failure. Although diuretics are commonly given to patients with heart failure due to cardiac amyloidosis, beta-blockers, calcium channel blockers, and ace inhibitors may be harmful. [05:55] Understanding the Wrong Answer Choices Calcitonin is associated with isolated amyloidosis of the thyroid. Prolactin is associated with lactation found in amyloidosis that is isolated to the pituitary gland. Acetylcholine is the negative chronotropic sinoatrial node in the right vagus nerve. The stimulation of the nerve decreases the firing of the SA nodes, increasing potassium and decreasing sodium and calcium movement to the cell. Finally, immunoglobulin amyloid deposition is widespread and it's the result of its light chain immunoglobulin deposition. The point of the question was that isolated amyloidosis can affect many particular organs. This is different from more widespread amyloidosis related to immunoglobulin in terms of ideology and distribution. [07:10] The Big Takeaway Amyloid is not just that atrial natriuretic factor but you have to ask yourself where is it is as you're reading this question. Is it in the parathyroid for prolactin or widespread for the immunoglobulin or is it in the atrium for the atrial natriuretic peptide? [08:11] BoardVitals Check out BoardVitals for their Step 1 and Level 1 QBanks. Use the promo code BOARDROUNDS to save 15% off. This can be used for your SHELF exam QBanks as well. Links: BoardVitals

2019/7/31
09:10
26: Why Is This Menstruating Patient So Sick?

26: Why Is This Menstruating Patient So Sick?

Session 26 A 20-year-old menstruating adult is tachycardic, somnolent, and hypotensive with GI symptoms and macular rash. What sort of organism do you suspect? As always, we're joined by Dr. Karen Shackelford from BoardVitals. Listen to this podcast episode with the player above, or keep reading for the highlights and takeaway points. [01:35] Question of the Week A 20-year-old female patient presents 5th day of her menstrual period complaining about abdominal pain, vomiting, watery diarrhea, and myalgia for 12 hours. On exam, her temperature is 103.13 F. Her blood pressure is 80/60 mm/Hg. And her heart rate is 135 beats per minute. She is ill-appearing, somewhat somnolent, has hyperemic 02:04 and a generalized erythematous macular rash that involves her palms and soles. Which of the following best describes the cause of her illness? (A) Gram-negative diplococci (B) Gram-negative obligate intracellular bacteria (C) Gram-positive facultative anaerobic cocci (D) Single positive stranded RNA virus [Related episode: Biology Grab Bag of Questions for the MCAT] [02:50] Thought Process Behind the Correct Answer The correct answer here is C. The patient has toxic shock syndrome. It didn't mention in the question but she had an indwelling tampon. Highly absorbent tampons are the biggest risk factor. But interestingly, half of the women who develop toxic shock syndrome during the menstrual period are not using tampons actually. Related to the menstrual period, however, a toxic shock is usually the result of infection by Staphylococcus aureus. It releases endotoxins. But also, 05:33 axis is superantigen. And that's what triggers the syndrome. It triggers the activation of T-lymphocyte and they release massive amounts of cytokine. The post-immune response is limited in patients with toxic shock. Studies show that people who end with toxic shock, they failed to develop an antibody against the bacteria that usually developed in up to 95% of the population in childhood. The criteria for diagnosis include fever, chills, hypotension, and dermatologic findings. Evident multi-system organ involvement is at least 3 body systems and that counts the skin. In this patient's case, she had her circulatory system. She had hyperemia of her mucus membranes. The maculopapular rash would eventually desquamate after 1-2 weeks. She had nausea, vomiting, diarrhea in the GI system. Her mental status was somnolent. Some people have seizures from somnolence or encephalopathy that the other organ involvement may include intrinsic renal failure or prerenal failure. Myalgias are also sometimes resolved in elevated serum creatinine phosphokinase. hepatic dysfunction is also not uncommon. [07:50] The Treatment If there's foreign body removal, the treatment of any surgical wounds is the rapid administration of appropriate antibiotics. This includes Vancomycin and Clindamycin with the Penicillin that has B-lactamase inhibitor. [08:10] Understanding the Wrong Answer Choices You would probably suspect meningococcal meningitis but then you would have thought they would have given you a clue about the stiff neck. Rocky Mountain spotted fever for answer choice B would also be a good thought. The USMLE Step 1 is going to give you clues to the most typical case. For instance, with Rocky Mountain spotted fever, they would probably mention that the patient was in an endemic area. But they wouldn't necessarily say he was bitten by a mosquito. Finally, Dengue fever is the diagnosis for answer choice D. Remember that they're not going to hand-feed you every single detail. It's not always

2019/7/24
12:22
25: What will we See with Potential Pediatric Infection?

25: What will we See with Potential Pediatric Infection?

Session 25 Dr. Karen Shackelford form BoardVitals joins us once again as we dig deep into a question about the hematopoietic and immune system. Listen to this podcast episode with the player above, or keep reading for the highlights and takeaway points. [01:05] About BoardVitals If you're ready to prepare for your Step 1 or Level 1, go to BoardVitals. Their QBank system is set up to simulate the real USMLE Step 1 and COMLEX Level 1 exams. They have questions that are equally as hard to get you prepared for your exam. Use the promo code BOARDROUNDS to save 15% off when you purchase any of their products. [02:20] Question of the Week A 16-year-old male presents with a complaint of sore throat, fatigue and low-grade fever for three days. Exam reveals glossopharyngeal erythema with white exudates on his tonsils. He has enlarged posterior cervical lymph nodes and the posterior auricular lymph nodes are slightly enlarged. His spleen is palpable on abdominal exam. The throat culture is negative for strep and the monospot is positive. Which of the following findings are associated with the patient's diagnosis? (A) Atypical lymphocyte (B) Eosinophilia (C) Howell-Jolly bodies (D) Sickled erythrocytes (E) Target cells [Related episode: USMLE and COMLEX Prep: Glossopharyngeal Nerve Anatomy] [03:20] Thought Process Behind the Right Answer The correct answer here is A. The enlarged spleen could throw students off as it may make you think about Howell-Jolly bodies. But this is a case of classical mononucleosis with fever, exudative pharyngitis, the tender lymphadenopathy, particularly posterior in the cervical and posterior auricular nodes. Adenopathy in the anterior nodes and the atypical lymphocytosis are the hallmarks of classic infectious mononucleosis. The explanation to this question goes on to discuss the infection of the Epstein-Barr virus. It's a viral replication that begins in the oral pharyngeal epithelial cells with dissemination and infection of B-lymphocytes and the oropharyngeal lymphoid tissue. There is more Step 1 detail here. The infected B-lymphocytes produce antibodies to the viral antigens. But they also produce another type of antibody which could be heterophile antibodies that are not antibodies to the virus, but antibodies to other tissues. Active infection and the reinfection are regulated basically by the Epstein-Barr virus-specific T-lymphocyte. And atypical lymphocytes are activated. CDA plus T-cells and CD16 after killer cells appear in the blood at least 1-3 weeks after symptom onset. Fatigue can persist forever – 6 months or longer in 13% of patients. The splenic enlargement is a big caution for practitioners to remind their patients to avoid contact. The enlargement usually resolves after about 3 weeks. But even without contact, spontaneous splenic rupture is responsible throughout half of the cases. This usually occurs 2 weeks after symptom onset. [06:50] Understanding the Other Answer Choices Eosinophilia is usually associated with parasitic infection. The Howell-Jolly bodies were good distractor. They refer to the basophilic remnants of DNA. The circulating erythrocyte is usually removed in the spleen so they're found in patients who have either no spleen or 07:15. Sickled erythrocytes are associated with sickle cell disease. Target cells are associated with this disorder where the erythrocyte's cell surface is increased disproportionately to the cell volume. An example would be spherocytosis. Links:

2019/7/17
09:22
24: The Mechanism of Hepatitis D Superinfection

24: The Mechanism of Hepatitis D Superinfection

Session 24 We're joined by Dr. Karen Shackelford from BoardVitals as we talk about hepatitis and how antigens and antibodies appear and disappear during the course of infection. Please also check out Specialty Stories, a podcast dedicated to helping you figure out what specialty you want to practice. Listen to different physicians as I interview them about why they chose their specialty, what they like and don't like about it, and much more. Maximize your Step 1/Level 1 prep by checking out BoardVitals. Check out their 3 or 6-month plan where you get access to there over 1700-question QBank. Get detailed explanations and rationales for every question targeted to the Boards. Use the promo code BOARDROUNDS to save 15% off. Listen to this podcast episode with the player above, or keep reading for the highlights and takeaway points. [02:20] Question of the Week A 45-year-old male presents a sudden onset of flu-like symptoms and yellowing eyes which he thought looks scary to him when he saw his reflection on the mirror. His past medical history reveals positive Hepatitis B infection and his lab's elevated ALT and AST levels. The consult suspects that he may not be superinfected with Hepatitis D. Hepatitis D virus can only propagate in the presence of Hepatitis B. The presence of which of the following components of Hepatitis B viral protein is necessary to allow Hepatitis D infection? (A) HpX (pX antigen) (B) Hepatitis B core antigen (HBcAg) (C) Hepatitis B surface antigen (D) Hepatitis B  e-antigen (E) Hepatitis B virus DNA polymerase [Related episode: What Does Academic Infectious Disease Look Like?] [03:35] Thought Process Behind the Correct Answer The correct answer here is C. Remember the actual viral structures. Hepatitis D envelops single-stranded RNA virus. It can't make its own surface antigens. So it requires Hepatitis B surface antigen. Hepatitis D can only be acquired either by co-infection or superinfection of an HPV carrier of co-infection. But this only resolves in 2% of the cases. HPV is a virulent pathogen.  Superinfection results in chronic hepatitis in over 90% of cases. Often, hepatitis with rapid progression of cirrhosis in about 80% of cases. But the influx of this type of viral infection has significantly declined since the development and widespread use of the Hepatitis B vaccine. However, this is still a problem in developing countries. In a lot of underdeveloped countries, it's passed on through migrants from more developed countries. It's therefore important for people to be aware of their Hepatitis B immunity and their potential for this really virulent superinfection. [Related episode: USMLE and COMLEX Prep: Tropical Medicine—Dengue Fever] [07:35] Understanding the Wrong Answer Choices Hepatitis pX is pX protein of Hepatitis B virus. It's implicated in viral transcription, replication, and increased risk of hepatocellular carcinoma through the expression of this X protein gene. The core antigen is the indicator of active viral replication. It's also a determinant of whether an individual is able to transmit the infection. But this is not the necessary component for the protein. Hepatitis B e-antigen can act as a marker of our replication infectivity but this isn't the necessary component either. Hepatitis B virus DNA polymerase is not necessary for HPV to replicate. HPV is the host...

2019/7/10
09:57
23: Etiology of an Absent Nerve Reflex of the Palate

23: Etiology of an Absent Nerve Reflex of the Palate

Session 23 We're joined by Dr. Karen Shackelford from BoardVitals as we tackle a neuro question this week. Maximize your Step 1/Level 1 prep by checking out BoardVitals. They have an amazing QBank that contains targeted questions. If you have a question about a question or explanation, for instance, simply click a button. This will allow you to ask a doctor and get a response within 24-48 hours. Use the promo code BOARDROUNDS to save 15% off. Listen to this podcast episode with the player above, or keep reading for the highlights and takeaway points. [01:13] Question of the Week A patient has a decreased level of consciousness and they're testing the gag reflex. The elevation of the soft palate is symmetric when he touched the left side. But when he touched the right side, there's no response. Which of the following is true relating to this patient's condition? (A) The glossopharyngeal nerve carries efferent fibers that mediate the gag reflex. (B) The ideology of that absent reflex is a lesion of the right glossopharyngeal nerve. (C) The cause of the patient's absent reflex is a lesion of the left vagus nerve. (D) The reflex is mediated through the dorsal motor nucleus of the vagus. (E) Both the glossopharyngeal nerve and the vagus nerve are damaged on the right side. [Related episode: USMLE and COMLEX Prep: Glossopharyngeal Nerve Anatomy] [02:11] Thought Process Behind the Correct Answer The correct answer here is B. The motor limb is mediated by the vagus nerve. Sensory, however, is mediated by the glossopharyngeal nerve. The vagus nerve also carries some sensory fibers through the recurrent laryngeal. If the gag reflex is intact, the soft palate will rise symmetrically regardless of which side is touched. If both the glossopharyngeal and the vagus are damaged on one side, there is no response when touching the contralateral side. The soft palate will rise unilaterally on the side that's intact. Also, there won't be any response whenever you're testing the affected side of the lesion if both nerves are damaged. The vagus nerve is the only nerve damaged and there's a lesion on the single side of it. And the soft palate rises and pull to the intact side. Regardless of the pathway, this is something worth remembering. If the glossopharyngeal is only damaged on a single side, there's not going to be a response on either side when you test the reflex on the affected side. This is because you're not receiving the sensory impulse. Whenever you test the intact side, the palate will rise on both sides because the motor fibers of the vagus nerve are still intact. [06:40] Understanding the Other Answer Choices The afferent fibers of the glossopharyngeal nerve mediate the sensory component of the gag reflex. Hence, answer choice A is wrong. For C, if the left vagus nerve or the motor nerve was damaged on the left side resulting in an elevation of the soft palate on the right no matter which side was tested. In other words, this is the lateral lesion of vagus nerve. There's also the elevation of the soft palate to the contralateral side regardless of which side you're testing. For option D, this is also wrong because the reflex is mediated through the nucleus ambiguus. For E, if that were the case, then there would be no response at all when testing the right side or the side of the lesion. There would also be no response when testing the left side because the motor portion is damaged on the side of the lesion. Hence, there'd be an asymmetric elevation of the soft palate on the contralateral side. [08:45] BoardVitals Maximize your...

2019/7/3
09:50