An emergency department evaluation is requested for a 42-year-old man who reports severe, … — USMLE Step 2 CK

An emergency department evaluation is requested for a $42$ -year-old man who reports severe, diffuse abdominal pain that consistently begins $30\text{ minutes}$ after meals over the past $4\text{ weeks}$ . He also reports a $6\text{-kg}$ ( $13\text{-lb}$ ) weight loss during this period, diffuse muscle aches, and intermittent fevers. Two days ago, the patient developed difficulty lifting his right foot while walking. His temperature is $38.1^\circ\text{C}$ ( $100.6^\circ\text{F}$ ) and blood pressure is $168/98\text{ mmHg}$ . Physical examination shows a mottled, purplish, net-like rash on the lower extremities. Neurologic examination demonstrates $2/5$ motor strength in right foot dorsiflexion and decreased pinprick sensation over the right lateral calf.

Laboratory studies are as follows:

Laboratory Test	Result
Hemoglobin	$10.8\text{ g/dL}$
Leukocyte count	$12,500/\text{mm}^3$
Platelet count	$410,000/\text{mm}^3$
Blood urea nitrogen	$32\text{ mg/dL}$
Serum creatinine	$1.9\text{ mg/dL}$
Erythrocyte sedimentation rate	$78\text{ mm/h}$
Hepatitis B surface antigen	Positive

Urinalysis reveals $1+$ protein, $0-2$ red blood cells/hpf, and no cellular casts.

Which of the following is the most appropriate next step in diagnosis?

Mesenteric and renal angiographyAnswer
B
Percutaneous renal biopsy
C
Testing for antineutrophil cytoplasmic antibodies
D
Electromyography and nerve conduction studies
E
Colonoscopy with mucosal biopsy

Answer

The correct answer is mesenteric and renal angiography, which is the preferred diagnostic modality for polyarteritis nodosa (PAN) presenting with intra-abdominal and renal involvement.

The correct next step is mesenteric and renal angiography. This patient's clinical presentation—postprandial abdominal pain (intestinal angina), mononeuritis multiplex (foot drop), livedo reticularis, new-onset hypertension, and acute kidney injury—in the setting of chronic Hepatitis B infection is highly characteristic of polyarteritis nodosa (PAN). PAN is a systemic necrotizing vasculitis that primarily targets medium-sized muscular arteries. When intra-abdominal or renal involvement is prominent, mesenteric and renal angiography is the preferred diagnostic test. It classically reveals multiple microaneurysms and segmental narrowing (often described as a 'string of pearls' appearance) of the medium-sized arteries. Angiography provides a high diagnostic yield while entirely avoiding the significant bleeding risks associated with deep tissue biopsies.

Step-by-Step Solution

Identify the defining clinical features and vital sign abnormalities.

The patient presents with intestinal angina, mononeuritis multiplex (foot drop), livedo reticularis, fever, weight loss, and new-onset hypertension.

Recognizing this classic constellation of symptoms is essential for formulating a differential diagnosis of systemic vasculitis.

Interpret the laboratory findings in the context of the clinical picture.

The patient has elevated inflammatory markers, acute kidney injury without glomerulonephritis (no RBC casts), and a positive Hepatitis B surface antigen.

The absence of an active urinary sediment points away from small-vessel vasculitis, while Hepatitis B positivity strongly suggests polyarteritis nodosa (PAN), a medium-vessel vasculitis.

Determine the most appropriate diagnostic test based on the suspected disease mechanism.

Mesenteric and renal angiography is selected over biopsy.

In PAN, medium-sized muscular arteries develop microaneurysms that are clearly visible on angiography. A renal biopsy carries a high risk of life-threatening hemorrhage from these aneurysms and has low yield because it primarily samples the unaffected glomeruli.

Key Concept

Polyarteritis nodosa (PAN) is a medium-vessel necrotizing vasculitis strongly associated with Hepatitis B, frequently causing renal insufficiency without glomerulonephritis and mesenteric ischemia. It is best diagnosed with mesenteric and renal angiography to identify characteristic microaneurysms.

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