Unusual presentation of polyarteritis nodosa.

Area of Science:

• Vascular pathology
• Rheumatology
• Musculoskeletal disorders

Background:

• Polyarteritis nodosa (PAN) is a systemic vasculitis typically affecting medium-sized arteries.
• Localized forms of PAN are uncommon, and calf muscle involvement is particularly rare.
• Understanding atypical presentations is crucial for timely diagnosis and management.

Observation:

• A patient presented with sudden, severe calf pain, initially mimicking musculoskeletal injury.
• Gastrocnemius muscle and fascia biopsies revealed acute necrotizing arteritis and fasciitis.
• Affected blood vessels showed lumen occlusion by thrombi.

Findings:

• This case represents an unusual localized form of polyarteritis nodosa affecting the calf.
• Evidence of fascial involvement in calf PAN is reported for the first time, potentially explaining symptom severity.
• Multiple intraluminal thrombi and anticardiolipin antibodies suggested a coexisting coagulopathy, contributing to pain intensity.

Implications:

• Highlights the importance of considering vasculitis in unexplained severe limb pain.
• Suggests fascial involvement may exacerbate clinical features in localized PAN.
• Underscores the potential role of coagulopathies in the presentation and severity of PAN.