The presence of isolated IgM deposits in the skin is currently called cutaneous macroglobulin–osis (CM), and a bullous disease form that results from immunoglobulin deposition on the basal membrane has been reported.21- 25 Because only 6 previous cases have been published to date, CM is considered a rare clinical manifestation of WM (Table). Age and sex distribution of the patients, including our 2 patients, are within the normal range for WM, with a male predominance (75%) and a median age of 61.9 years (range, 48-73 years). The most frequently observed lesions were papules, sometimes associated with nodules and/or plaques. The evolution of disease in patient 2 was atypical, with progressive development of confluent, necrotic, and ulcerated plaques. A neoplastic B-cell infiltrate and/or an infectious disease was evoked, but histologic analysis revealed massive IgM deposits with transepidermal elimination. Transepithelial elimination was previously described in 3 patients with CM, with lesions that presented as necrotic and crusted papules. In the setting of CM, skin lesions commonly appear on the knees, buttocks, and extensor surfaces of the lower and upper limbs, as in our 2 patients. Occasionally, lesions can be found on the trunk, face, neck, and scalp. Histologic examination of a skin biopsy specimen provides the diagnosis: a dense, eosinophilic, amorphous, strongly PAS-positive material fills the dermis. The search for amyloid deposits is negative (Congo red and thioflavine T stains; original magnification, ×10 and ×20, respectively). Deposits of IgM in the skin are demonstrated by immunofluorescence and immunohistochemical analysis.