Diagnosis: Polyarteritis Nodosa

The patient was treated with broad-coverage antibiotics, but all cultures were negative for organisms and they were discontinued. 

A biopsy was preformed of the skin nodule and revealed a neutrophilic panniculitis. An oral prednisone course was started. Panels for antinuclear antibodies, hepatitis, c-ANCA, and p-ANCA were negative. 

The histopathologic diagnosis included PAN, alpha-1 antitrypsin deficiency, infectious panniculitis, and erythema induratum. As special stains for bacteria, fungus, and mycobacteria were all negative, the diagnosis was most consistent with polyarteritis nodosa (PAN).

PAN is an autoimmune necrotizing vasculitis that affects small and medium sized arteries. Patients often present with painful cutaneous nodules, and ulceration can occur.  Livedo reticularis may also be present. Lesions commonly occur on the lower extremities, often below the knee (dependent areas). 

The cause of PAN is unknown, but it has been associated with many infections and chronic inflammatory conditions, such as hepatitis B and C, streptococcal infection, systemic lupus erythematosus, and hairy cell leukemia.

In 20% of patients with PAN, p-ANCA is positive. Systemically, PAN can cause dilatation and stenosis of the arteries of the kidney and mesentery, and can affect muscles, joints, and nerves. Urinalysis, visceral angiography, nerve function tests, and elevated ESR and CRP levels may provide important diagnostic information if systemic involvement is suspected.

Histopathology will reveal an inflammatory necrotizing arteritis of small and medium-sized vessels with focal panniculitis. Systemic corticosteroids are the mainstay of treatment. Occasionally, immunosuppressive drugs such as cyclophosphamide or azathioprine as used, although the data on efficacy of these medications is less clear. 

The patient had improvement of his lesions with corticosteroids.

The case was submitted by Dr. Susannah McClain of the University of Maryland Medical Center in Baltimore. Attending physicians were Dr. Anthony Gaspari and Dr. Grace Kao.