A 40-year-old woman with a history of seropositive rheumatoid arthritis presents with erythematous papules and plaques over the extensor surfaces of her arms. A skin biopsy reveals the findings seen below.

No evidence of vasculitis is seen. Direct immunofluorescence is negative. Which of the following best describes the diagnosis?

A. Necrobiosis lipoidica
B. Palisaded and neutrophilic granulomatous dermatitis
C. Interstitial granuloma annulare
D. Leukocytoclastic vasculitis
E. Rheumatoid nodule

Rationale: 

Granulomatous dermatoses with interstitial and palisaded patterns represent a diagnostic challenge and require careful correlation between histologic findings and clinical context. Key features such as the presence of neutrophils, necrobiosis, collagen degeneration, and the distribution of inflammation can help narrow the differential. Clinical context such as presence or absence of underlying disease often provides helpful information. 

Correct Answer: B. Palisaded and neutrophilic granulomatous dermatitis (PNGD)

PNGD shows a combination of palisading histiocytes, degenerating collagen, nuclear dust from neutrophils, and sometimes mucin. Unlike granuloma annulare or necrobiosis lipoidica, neutrophils are a prominent feature. The association with rheumatoid arthritis, as in this case, is typical. These lesions often respond to treatment of the underlying systemic disease.

Incorrect answers: 

A. Necrobiosis lipoidica is usually associated with diabetes mellitus and presents with yellowish plaques on the shins. Histologically, it shows layered necrobiosis, plasma cells, and thickened blood vessels, but neutrophils are not a prominent feature, and lesions are more chronic and atrophic.

C. Interstitial granuloma annulare presents with asymptomatic, annular plaques and shows interstitial histiocytic infiltrates with mucin, but lacks neutrophils or nuclear dust. It is usually not associated with systemic diseases.

D. Leukocytoclastic vasculitis is characterized by palpable purpura, especially on the legs, and shows fibrinoid necrosis of vessel walls, red blood cell extravasation, and nuclear debris in and around blood vessels. The biopsy in this case lacks vasculitic changes.

E. Rheumatoid nodule is found in patients with rheumatoid arthritis. These lesions show a central area of necrosis with surrounding palisading histiocytes but do not typically contain neutrophils or interstitial inflammation. They are often subcutaneous nodules over pressure points.

Additional reading at Chapter 6: Nodular and Diffuse Cutaneous Infiltrates