During a routine follow-up for chronic hepatitis B infection, a 45-year-old male construct… — USMLE Step 2 CK

During a routine follow-up for chronic hepatitis B infection, a 45-year-old male construction worker reports a 6-week history of intermittent fevers, severe muscle aches, and an unintentional $6$ kg ( $13$ lb) weight loss. He also describes a new, crampy abdominal pain that predictably begins 30 to 45 minutes after every meal. Yesterday, he stumbled while walking and noticed difficulty lifting his right foot. His hepatitis B is currently untreated.

Vital signs show a temperature of $38.2^\circ\text{C}$ ( $100.8^\circ\text{F}$ ), blood pressure of $168/102$ mmHg, and heart rate of $98$ /min. Neurologic examination reveals 2/5 strength in right ankle dorsiflexion and decreased pinprick sensation over the dorsum of the right foot. Skin examination demonstrates a violaceous, net-like pattern over both lower extremities.

Laboratory Test	Result
Leukocyte count	$14,500/\text{mm}^3$
Hemoglobin	$11.2 \text{ g/dL}$
Platelet count	$450,000/\text{mm}^3$
Blood urea nitrogen	$34 \text{ mg/dL}$
Serum creatinine	$2.1 \text{ mg/dL}$ (baseline $0.9 \text{ mg/dL}$ )
Erythrocyte sedimentation rate	$85 \text{ mm/h}$
Urinalysis	$1+$ protein, no red blood cells or casts

Which of the following is the most appropriate next step in the diagnosis of this patient's condition?

Mesenteric angiographyAnswer
B
Antineutrophil cytoplasmic antibody (ANCA) titer
C
Non-contrast computed tomography of the abdomen
D
Blood cultures and empiric intravenous ceftriaxone
E
Echocardiography and intravenous furosemide

Answer

Mesenteric angiography

The correct diagnostic test is mesenteric angiography. This patient's clinical presentation—intermittent fevers, weight loss, mononeuritis multiplex (foot drop), livedo reticularis, new-onset hypertension, renal insufficiency without glomerulonephritis, and postprandial abdominal pain—is highly characteristic of Polyarteritis Nodosa (PAN). PAN is a systemic necrotizing vasculitis that affects medium-sized muscular arteries and has a strong association with chronic hepatitis B virus (HBV) infection (present in up to 30% of cases). The renal involvement in PAN is due to arteritis of the renal vessels, which leads to ischemia, activation of the renin-angiotensin-aldosterone system, and severe hypertension. Notably, it spares the pulmonary vessels and the glomeruli, explaining the absence of red blood cell casts in the urine. Intestinal angina occurs due to mesenteric arteritis. When a biopsy of an affected organ (such as skin or a peripheral nerve) is not feasible or conclusive, abdominal (mesenteric and renal) angiography is the diagnostic test of choice. It classically reveals multiple microaneurysms and focal narrowing of medium-sized vessels, often described as a 'string of pearls' or 'rosary' appearance.

Step-by-Step Solution

Analyze the patient's systemic presentation and past medical history.

The patient has constitutional symptoms (fever, weight loss) and untreated chronic Hepatitis B infection.

Systemic symptoms in the setting of Hepatitis B strongly suggest an extrahepatic manifestation, particularly Polyarteritis Nodosa (PAN).

Evaluate the localized signs and organ involvement.

Findings include mononeuritis multiplex (foot drop), mesenteric ischemia (postprandial abdominal pain), livedo reticularis, and renal involvement (hypertension, elevated creatinine) without glomerulonephritis.

This specific pattern of organ involvement localizes the pathology to medium-sized muscular arteries, characteristic of PAN.

Determine the most appropriate diagnostic test.

Mesenteric angiography is the correct next step.

When tissue biopsy is not performed, angiography of the abdominal vessels confirms PAN by revealing classic microaneurysms and arterial cutoffs.

Key Concept

Diagnosis of Polyarteritis Nodosa (PAN) using angiography to visualize medium-vessel microaneurysms.

Estimated Time:2m 0s

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