COMSA Phase 1 Form 114 Practice Exam 176 Questions and Answers | Detailed Rationales | Study Guide

COMSA Phase 1 Form 114 Practice Exam 176 Questions and Answers | Detailed Rationales | Study Guide Question 1 – Microbiology / Infectious Disease A 72-year-old male with a history of poorly controlled diabetes mellitus presents with a 2-day history of fever, chills, and productive cough. Sputum culture grows a gram-negative coccobacillus that produces a greenish pigment on blood agar. The organism is oxidase-positive and grows on MacConkey agar. Which virulence factor is most directly responsible for the characteristic pigment production? A) Pyocyanin B) Pyoverdine C) Rhamnolipid D) Exotoxin A Correct Answer: B Rationale: Pyoverdine is a siderophore produced by Pseudomonas aeruginosa that fluoresces greenish-yellow under ultraviolet light and is responsible for the characteristic greenish pigment on culture media. This organism is a common cause of pneumonia in diabetic and immunocompromised patients. Question 2 – Biochemistry / Metabolism A 6-month-old infant presents with failure to thrive, vomiting, and lethargy after feeding. Laboratory studies reveal severe metabolic acidosis with an elevated anion gap. Urine organic acids show elevated methylmalonic acid and homocysteine. Which vitamin deficiency is most likely implicated in this presentation? A) Vitamin B1 B) Vitamin B6 C) Vitamin B9 D) Vitamin B12 Correct Answer: D Rationale: Methylmalonic aciduria with homocystinuria is classic for vitamin B12 (cobalamin) deficiency, which is required as a cofactor for methylmalonyl-CoA mutase and methionine synthase. This presentation in infancy suggests an inherited disorder of cobalamin metabolism. Question 3 – Pharmacology / Hematology A 45-year-old woman undergoing treatment for chronic myeloid leukemia develops progressive fatigue and bruising. Complete blood count shows pancytopenia with 2% blasts in the peripheral smear. Bone marrow biopsy reveals 25% blasts with Auer rods. She is started on a tyrosine kinase inhibitor that specifically targets the BCR-ABL fusion protein. Which medication is most appropriate? A) Dasatinib B) Bosutinib C) Ponatinib D) Imatinib Correct Answer: D Rationale: Imatinib is the first-line tyrosine kinase inhibitor for chronic myeloid leukemia that selectively inhibits the BCR-ABL fusion protein, leading to apoptosis of malignant cells. It is most appropriate for chronic-phase CML and has shown remarkable efficacy in achieving cytogenetic remission. Question 4 – Cardiology / Pathophysiology A 62-year-old male with a 30-pack-year smoking history presents with progressive dyspnea on exertion and a dry cough. Physical examination reveals jugular venous distension, hepatomegaly, and peripheral edema. Echocardiography demonstrates a thickened, rigid pericardium with diastolic dysfunction. Which hemodynamic finding is most characteristic of this condition? A) Decreased right atrial pressure B) Increased pulmonary wedge pressure C) Equalization of diastolic pressures D) Elevated cardiac output Correct Answer: C Rationale: Constrictive pericarditis is characterized by equalization of diastolic pressures across all four chambers of the heart due to the rigid pericardium limiting ventricular filling. This results in a dip-and-plateau pattern on pressure tracings and accounts for the signs of right-sided heart failure. Question 5 – Endocrinology / Physiology A 28-year-old female presents with weight loss, heat intolerance, and palpitations. Her thyroid-stimulating hormone (TSH) is undetectable, and free T4 is markedly elevated. Serum thyroid receptor antibodies are positive. She is started on an antithyroid medication that works by inhibiting thyroid peroxidase. After 3 months of treatment, she develops agranulocytosis. Which medication was most likely prescribed? A) Propylthiouracil B) Methimazole C) Carbimazole D) Potassium iodide Correct Answer: B Rationale: Methimazole is a thioamide that inhibits thyroid peroxidase and is associated with agranulocytosis as a rare but serious adverse effect. It is often preferred over propylthiouracil for Graves’ disease due to a more favorable side-effect profile, though both can cause this complication. Question 6 – Neurology / Pharmacology A 55-year-old man with chronic migraines presents to the emergency department with a severe, unilateral, throbbing headache associated with nausea, photophobia, and phonophobia. He has failed treatment with oral triptans and NSAIDs. Which medication administered intravenously would be most appropriate for acute migraine management in this patient? A) Valproic acid B) Dihydroergotamine C) Propranolol D) Topiramate Correct Answer: B Rationale: Dihydroergotamine is a parenteral medication effective for acute migraine treatment, particularly in patients who have failed oral therapies. It acts as a 5-HT1B/1D receptor agonist with vasoconstrictive properties and anti-inflammatory effects, and is administered intravenously or intramuscularly. Question 7 – Gastroenterology / Immunology A 34-year-old woman with a history of autoimmune thyroiditis presents with episodic abdominal pain, diarrhea, and flushing. She is found to have elevated serum chromogranin A levels and a 2-cm mass in the ileum on abdominal CT. Biopsy reveals nests of uniform cells with positive staining for synaptophysin and cytokeratin. Which hormone is most likely responsible for her symptoms? A) Gastrin B) Serotonin C) Histamine D) Calcitonin Correct Answer: B Rationale: Serotonin is the primary mediator of symptoms in carcinoid syndrome, which presents with flushing, diarrhea, and abdominal pain. This neuroendocrine tumor originates from enterochromaffin cells in the gastrointestinal tract, and serotonin excess accounts for the classic symptoms. Question 8 – Pulmonary / Critical Care A 70-year-old male with end-stage chronic obstructive pulmonary disease requires mechanical ventilation for acute hypercapnic respiratory failure. Initial arterial blood gas on assist-control ventilation shows pH 7.28, PaCO2 62 mmHg, and PaO2 78 mmHg. Which ventilator setting should be adjusted to correct his acidosis? A) Increased respiratory rate B) Decreased tidal volume C) Increased FiO2 D) Decreased PEEP Correct Answer: A Rationale: Increasing the respiratory rate will increase minute ventilation, thereby reducing PaCO2 and correcting respiratory acidosis. This is the most direct intervention for hypercapnia in a patient receiving mechanical ventilation with otherwise adequate oxygenation. Question 9 – Immunology / Rheumatology A 45-year-old female presents with a malar rash, photosensitivity, oral ulcers, and non-erosive arthritis. Laboratory tests reveal antinuclear antibodies (ANA) positive at 1:640 with a homogeneous pattern, and anti-dsDNA antibodies are elevated. She develops proteinuria and hypertension. Which immune complex deposition pattern is most characteristic of her renal involvement? A) Linear deposition along the glomerular basement membrane B) Granular deposition in the mesangium and capillary loops C) Electron-dense deposits in the subepithelial space D) No immune deposits by immunofluorescence Correct Answer: B Rationale: Lupus nephritis (class IV) demonstrates granular deposition of immune complexes in the mesangium and capillary loops on immunofluorescence. This pattern corresponds to “full house” immunofluorescence with IgG, IgA, IgM, C3, and C1q deposits, leading to proliferative glomerulonephritis. Question 10 – Infectious Disease / Microbiology A 32-year-old man who recently returned from a camping trip in the Pacific Northwest presents with a fever, myalgias, and a characteristic erythema chronicum migrans rash on his thigh. He is diagnosed with Lyme disease. Which antibiotic is contraindicated in this patient if he is also taking a medication that prolongs the QT interval? A) Doxycycline B) Amoxicillin C) Cefuroxime axetil D) Azithromycin Correct Answer: D Rationale: Azithromycin is a macrolide antibiotic that can prolong the QT interval and increase the risk of torsades de pointes, particularly when used with other QT-prolonging medications. It is not the first-line treatment for early Lyme disease, with doxycycline or amoxicillin being preferred. Question 11 – Renal / Fluid and Electrolytes A 68-year-old woman with heart failure on furosemide therapy presents with weakness, muscle cramps, and a serum potassium level of 3.0 mEq/L. Her ECG shows prominent U waves. Which compensatory mechanism is activated in response to this electrolyte disturbance? A) Increased aldosterone secretion B) Decreased renin release C) Increased antidiuretic hormone D) Decreased sympathetic tone Correct Answer: A Rationale: Hypokalemia stimulates aldosterone secretion directly, which promotes renal potassium wasting and exacerbates the hypokalemia. Aldosterone secretion is also driven by the renin-angiotensin system in response to volume depletion, further complicating the electrolyte imbalance. Question 12 – Hematology / Oncology A 67-year-old male presents with fatigue, night sweats, and unintentional weight loss. Peripheral blood smear shows lymphocytosis with characteristic “smudge cells.” Flow cytometry reveals CD5+, CD19+, CD20+, and CD23+ cells with dim surface immunoglobulin. Which finding on bone marrow biopsy is most diagnostic of this condition? A) More than 20% blasts with Auer rods B) Diffuse infiltration of small mature lymphocytes C) Ringed sideroblasts with Prussian blue stain D) Sheets of atypical plasma cells with Russell bodies Correct Answer: B Rationale: Chronic lymphocytic leukemia (CLL) is characterized by the accumulation of mature-appearing B lymphocytes with a characteristic immunophenotype. Bone marrow biopsy shows diffuse infiltration by these small lymphocytes, and peripheral blood requires 5000 monoclonal B lymphocytes per microliter for diagnosis. Question 13 – Psychiatry / Neurology A 24-year-old college student presents with complaints of difficulty concentrating, excessive daytime sleepiness, and episodes of sudden loss of muscle tone when laughing. She reports vivid hallucinations upon falling asleep. Which neurotransmitter imbalance is most implicated in her condition? A) Decreased histamine in the ventrolateral preoptic nucleus B) Decreased orexin in the lateral hypothalamus C) Increased dopamine in the ventral tegmental area D) Decreased serotonin in the raphe nucleus Correct Answer: B Rationale: Narcolepsy with cataplexy results from loss of orexin (hypocretin)-producing neurons in the lateral hypothalamus. Orexin deficiency leads to impaired wakefulness regulation, resulting in excessive daytime sleepiness, cataplexy, and hypnagogic hallucinations.