Calcinosis cutis may manifest with subcutaneous nodules over joints that discharge white material. The condition may be idiopathic, metastatic secondary to hypercalcemia, or associated with diseases such as dermatomyositis and systemic scleroderma. On histologic examination, calcinosis cutis demonstrates deposits of deeply basophilic material in the dermis or subcutaneous tissue. The deposits stain black with von Kossa staining.
Tuberous xanthomas may manifest with large nodules on the elbows, most commonly in patients with hyperlipidemia. On histologic examination, the lesions demonstrate diffuse dermal aggregates of foam cells, which represent lipid-laden macrophages. Inflammation is minimal. The lipid within the foam cells can be highlighted with oil red O staining of frozen sections.
Granuloma annulare manifests with papular lesions on the extremities, and deep granuloma annulare may form nodular lesions. On histologic examination, granuloma annulare is characterized by foci of altered connective tissue in the dermis, which often contain mucin and are surrounded by a palisade arrangement of histiocytes. The mucin in the center of the palisade areas forms so-called blue granulomas.
On formalin-fixed biopsy specimens, gouty tophi demonstrate aggregates of amorphous white material, which are often walled off by a rim of macrophages and multinucleated giant cells. On high-power views, the amorphous material displays needle-shaped, radial clefts, where the urate crystals have dissolved.
Rheumatoid nodules may occur as nodular lesions over joints, similar to gout. On histologic examination, rheumatoid nodules demonstrate areas of histiocytes in a palisade arrangement that surround areas of necrobiosis and fibrin within the deep dermis and subcutis. The central necrobiotic areas are usually homogeneous and eosinophilic, forming “red granulomas.”
