Pathogenesis of paraneoplastic follicular hyperkeratotic spicules in multiple myeloma. Follicular and epidermal accumulation of IgG dysprotein and cryoglobulin.

We describe a 62-year-old man with multiple myeloma who developed horny spicules on his face, particularly on his nose. IgG-lambda monoclonal gammopathy was detected, and the serum dysprotein was shown to be a cryoglobulin, which forms a cryogel at low temperatures. Light and electron microscopic and immunohistochemical examinations showed an intercellular precipitation and massive accumulation of the IgG dysprotein and cryoglobulin between the keratinocytes of the upper epidermis and the infundibular epithelium. The follicles were dilated and filled with parakeratotic cells, the protein deposits between them and a rudimentary hair thus resulting in the clinically visible symptoms of horny spicules. The limitation or the predominance of the symptoms in cold-exposed body regions, the morphological identification of the dysprotein deposits as cryoglobulin or cryogel, and the laboratory findings concerning the temperature and pH dependence of the precipitation of the IgG dysprotein reveal that the paraneoplastic horny spicules are a hitherto unknown clinical manifestation of cryoglobulinemia.