DFT-MEDICINE D5-13-10-2025-MAXEMO

The molecular mimicry responsible for carditis following streptococcal pharyngitis involves structural homology between a bacterial surface component and human cardiac myosin. Which virulence factor of Streptococcus pyogenes is the primary driver of this autoimmune cross-reactivity?

• M protein

• Streptolysin O

• Hyaluronidase

• Lipopolysaccharide

Answer explanation

The M protein is the key virulence factor whose antigenic domains share homology with human cardiac myosin and valve proteins, leading to the production of cross-reactive antibodies that cause carditis.

A patient with long-standing, poorly controlled diabetes mellitus and background retinopathy presents with nephrotic-range proteinuria. A renal biopsy shows prominent, acellular, PAS-positive nodules in the mesangial regions of the glomeruli. Which of the following best describes this characteristic lesion?

• Kimmelstiel-Wilson lesions

• Subepithelial "humps"

• "Spike and dome" formation

• Linear deposition of IgG

Answer explanation

 Kimmelstiel-Wilson lesions. This is the classic pathognomonic finding for nodular glomerulosclerosis in diabetic nephropathy, characterized by eosinophilic, PAS-positive mesangial nodules, consistent with the clinical history.

A patient presents with altered mental status and severe metabolic acidosis with a high anion gap after ingesting an unknown substance. He develops acute oliguric renal failure. Urinalysis reveals the presence of envelope-shaped crystals. Which substance is the most likely cause of this presentation?

• Ethylene glycol

• Methanol

• Salicylate

• Lithium

Answer explanation

Ingestion of ethylene glycol (found in antifreeze) causes high anion gap metabolic acidosis. Its metabolite, oxalic acid, precipitates with calcium in renal tubules, forming calcium oxalate crystals and causing acute tubular necrosis.

A patient admitted with septic shock remains hypotensive despite vasopressor support. On day 3, their serum creatinine increases from 0.9 mg/dL to 2.5 mg/dL. A urine sample reveals the following: Urine Sodium: 60 mmol/L, Urine Osmolality: 280 mOsm/kg, and Fractional Excretion of Sodium (FENa): 3%. Urine microscopy is significant for a specific finding. What is the most likely diagnosis?

• Acute Tubular Necrosis (ATN)

• Pre-renal Azotemia

• Acute Interstitial Nephritis (AIN)

• Post-renal Obstruction

Answer explanation

The patient’s findings of high urine sodium (>40), low urine osmolality (<350), and high FENa (>2%) in the setting of sepsis-induced hypotension strongly indicate established intrinsic renal damage, characteristic of ATN.

A patient develops acute kidney injury after an episode of bloody diarrhea, with labs confirming hemolytic uremic syndrome. Administration of which of the following is most likely to worsen the clinical outcome?

• Antibiotics

• Intravenous fluids

• Packed red blood cells

• Furosemide

Answer explanation

In Shiga toxin-producing E. coli (STEC)-HUS, antibiotics can lyse bacteria, increasing toxin release and worsening the endothelial injury and subsequent renal failure.

Assertion (A): Warfarin therapy is a significant, non-traditional risk factor for the development of calciphylaxis in patients with end-stage renal disease. Reason (R): Warfarin, a vitamin K antagonist, impairs the gamma-carboxylation of Matrix Gla Protein (MGP), a potent inhibitor of ectopic vascular calcification.

• Both A and R are true, and R is the correct explanation of A.

• Both A and R are true, but R is NOT the correct explanation of A.

• A is true, but R is false.

• Both A and R are false.

Answer explanation

The assertion is a known clinical association. The reason provides the precise molecular mechanism: warfarin's antagonism of vitamin K prevents the activation of MGP, a key protein that prevents calcium deposition in vessel walls.

A patient with Stage 4 Chronic Kidney Disease is being managed for various complications. Match the clinical problem in List I with its most appropriate corresponding management principle or pathological feature in List II.

• 1-p, 2-q, 3-r, 4-s

• 1-q, 2-p, 3-s, 4-r

• 1-p, 2-r, 3-q, 4-s

• 1-s, 2-r, 3-p, 4-q

Answer explanation

 anemia of CKD with an ESA (Darbepoetin), hyperphosphatemia with a phosphate binder (Sevelamer), the skin lesions with calciphylaxis (calcific uremic arteriolopathy), and low bicarbonate with metabolic acidosis.

A patient with Stage 5 CKD on maintenance hemodialysis presents with severe bone pain. Laboratory results show a serum calcium of 8.2 mg/dL, serum phosphate of 7.5 mg/dL, and an intact PTH level of 950 pg/mL. This constellation of findings is characteristic of ________, for which the most appropriate initial pharmacological intervention is the administration of ________.

• Secondary hyperparathyroidism; a non-calcium-based phosphate binder

• Adynamic bone disease; cinacalcet

• Osteomalacia; calcitriol

• Tertiary hyperparathyroidism; urgent parathyroidectomy

Answer explanation

The triad of hypocalcemia, hyperphosphatemia, and markedly elevated PTH is the hallmark of secondary hyperparathyroidism in CKD. The initial step is to control hyperphosphatemia, the primary driver of the process, using a phosphate binder.

A kidney transplant recipient presents with acute graft dysfunction. A biopsy showing C4d deposition in peritubular capillaries is diagnostic of ________, a process primarily mediated by ________.

• Antibody-mediated rejection; donor-specific antibodies

• Acute cellular rejection; T-lymphocytes

• BK virus nephropathy; polyomavirus replication

• Calcineurin inhibitor toxicity; drug-induced arteriopathy

Answer explanation

C4d is a complement split product that serves as the pathognomonic marker for antibody-mediated rejection, which is driven by circulating donor-specific antibodies.

A patient on hemodialysis via a tunneled left internal jugular catheter develops ipsilateral facial and arm edema. This strongly suggests the complication of ________, most commonly located in the ________.

• Central venous stenosis; brachiocephalic vein

• Catheter-related sepsis; catheter tip

• Arteriovenous fistula steal; distal extremity

• Dialysis disequilibrium syndrome; cerebral cortex

Answer explanation

Long-term catheter use causes endothelial injury and stenosis. A left-sided catheter must pass through the left brachiocephalic vein, a common site for stenosis leading to these specific unilateral venous congestion signs.