The histological and pathogenetic spectrum of cutaneous disease in monoclonal gammopathies

The dermatological disorders associated with monoclonal gammopathies are clinically heterogeneous and may be divided into four groups with distinctive pathogenetic mechanisms (a) specific (infiltrative) disorders including primary and secondary cutaneous plasmacytoma and cutaneous lymphoplasmacytic infiltration of Waldenström's disease (b) skin disorders because of the deposition of monoclonal immunoglobulin (M protein), including amyloidoisis macroglobulinemia cutis, light chain deposition of Randall's disease, follicular spicules of the nose, and cryoglobulinemia (c) skin disorders associated with monoclonal gammopathies, including highly associated (>50%), weakly associated (<50%) or anecdotal and (d) miscellaneous (non specific). In most cases, histopathology is crucial to confirm or to diagnose those skin conditions and is also very useful to understand their pathogenetic mechanisms.