Cutaneous macroglobulinosis. A case report with unique ultrastructural findings

Cutaneous macroglobulinosis is a rare cutaneous manifestation of Waldenström's macroglobulinemia. Lesions result from the direct deposition of macroglobulin in the skin and have been called IgM storage papules. A case of cutaneous macroglobulinosis with unique ultrastructural findings was studied.

Cutaneous macroglobulinosis is characterized by multiple flesh-colored papules on extensor skin surfaces. Histologically, there are dermal collections of eosinophilic hyaline material, simulating amyloid. The material is positive on periodic acid-Schiff staining. Amyloid stains are negative or equivocal. Electron microscopy reveals thick, nonbranching, 56-nm-wide, linear material with cross striations at 12-nm intervals. These ultrastructural findings differ from the three previously reported cases.

Cutaneous macroglobulinosis may be a rare presenting sign of Waldenström's macroglobulinemia. Deposits of macroglobulin in the skin result in a histologic picture that greatly resembles amyloid. Histochemical stains, direct immunofluorescence microscopy, and electron microscopy are useful tools that enable accurate diagnosis and help to distinguish cutaneous macroglobulinosis from other deposition disorders.