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Giant extramucosal verruciform xanthoma over a discoid lupus erythematosus plaque in a patient with systemic lupus erythematosus

with subnephrotic proteinuria. Clinically, PNM presents as asymptomatic papulonodules that mostly appear on the trunk and upper extremities, although the face and other locations can also be affected. The histological picture is dominated by marked dermal pallor, because of diffuse mucin deposition in the papillary and reticular dermis, and lacks the typical epidermal and interface changes of specific LE lesions. The pathogenesis of PNM is unknown. Increased synthesis of glycosaminoglycans induced by circulating autoantibodies or serum cytokines was suggested. A possible role for androgens has also been postulated, as PNM most frequently occurs in men, contrasting with the female predominance in SLE. Exposure to ultraviolet light appears to aggravate skin lesions and may act as a contributing factor. Cutaneous mucinoses comprise a vast group of disorders that may present with similar clinicopathological features, leading to confusion between them. In our patient, the presence of paraproteinemia and the initial absence of LE features hampered the correct diagnosis; only with long-term, thorough assessment was an accurate classification possible. The clinical response of PNM to treatment is variable but mainly unsatisfactory. A minority of patients show improvement with antimalarials, however, most of them require additional treatment with oral corticosteroids. Herein, we report a case of PNM associated with SLE, in which correct identification of this entity proved to be challenging. We therefore highlight the diagnostic difficulties in such cases and the importance of recognizing this atypical presentation, as to ensure an early diagnosis of the underlying disease.