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Difficulty: MediumFormulating a Differential Diagnosis

A 47-year-old man comes to the emergency department complaining of a 3-week history of recurrent fevers, a 6-kg (13.2-lb) weight loss, and diffuse muscle aches. Over the past 48 hours, he has experienced severe, crampy abdominal pain that consistently worsens approximately 30 minutes after meals. He also reports a new inability to lift his right foot while walking. His medical history is notable for an acute viral infection two months ago. He takes no medications.

Vital signs are as follows:
Temperature: 38.4°C (101.1°F)
Pulse: 108/min
Blood pressure: 165/100 mmHg
Respirations: 16/min

Physical examination reveals weakness with right ankle dorsiflexion and a purplish, lace-like reticular rash over both lower extremities. The abdomen is diffusely tender to palpation, but there is no rebound or guarding.

Laboratory results:
Leukocytes: 15,500/mm³
Hemoglobin: 11.2 g/dL
Platelets: 410,000/mm³
Erythrocyte sedimentation rate: 102 mm/hr
Creatinine: 1.9 mg/dL
Hepatitis B surface antigen: Positive
Hepatitis C virus antibody: Negative
Antineutrophil cytoplasmic antibodies (ANCA): Negative
Urinalysis: Normal (no blood, no protein)

Which of the following is the most likely diagnosis for this patient's current presentation?

  1. A
    Microscopic polyangiitis
  2. B
    Cryoglobulinemic vasculitis
  3. Polyarteritis nodosaAnswer
  4. D
    Infective endocarditis
  5. E
    Antiphospholipid syndrome

Answer

The most likely diagnosis is polyarteritis nodosa.
The correct answer accurately synthesizes the clinical presentation of medium-vessel vasculitis. The patient exhibits classic signs of polyarteritis nodosa (PAN): mesenteric ischemia causing postprandial abdominal pain (intestinal angina), mononeuritis multiplex causing foot drop, livedo reticularis, and renal involvement leading to hypertension and elevated creatinine. Crucially, PAN spares the capillary beds, meaning there is no glomerulonephritis, which aligns perfectly with the normal urinalysis. The presence of Hepatitis B surface antigen further cements this diagnosis, as Hepatitis B is a well-known risk factor for PAN.

Step-by-Step Solution

1
Identify the systemic inflammatory syndrome.
The patient has prominent constitutional symptoms (fevers, significant weight loss), marked leukocytosis, and an elevated erythrocyte sedimentation rate.
Recognizing severe systemic inflammation helps rule out simple mechanical, degenerative, or pure primary thrombotic etiologies.
2
Analyze specific organ system involvement.
The clinical findings include mononeuritis multiplex (foot drop), mesenteric ischemia (postprandial abdominal pain), renal involvement (hypertension, elevated creatinine), and livedo reticularis.
Localizing the pathology to multiple distinct vascular beds strongly suggests a systemic vasculitis.
3
Differentiate based on vessel size and laboratory clues.
The normal urinalysis (absence of RBC casts or protein) rules out capillary involvement (glomerulonephritis), distinguishing this condition from small-vessel vasculitides. The positive Hepatitis B surface antigen provides a classic epidemiological link.
Medium-vessel vasculitides like PAN spare the capillaries and have well-documented associations with viral hepatitis B.

Key Concept

Polyarteritis nodosa is a medium-vessel vasculitis characterized by constitutional symptoms, mononeuritis multiplex, livedo reticularis, mesenteric ischemia, and renal artery involvement (hypertension, kidney injury) without glomerulonephritis. It is strongly associated with Hepatitis B infection.
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Formulating a Differential Diagnosis

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