Eruptive xanthomata with urate-like crystals.

The microscopic manifestations of eruptive xanthomata are variable and although they are most frequently characterized by aggregations of foamy macrophages in the dermis, they can, on occasion, simulate granuloma annulare. We have recently encountered a further unusual histopathological variant of eruptive xanthomata in 3 skin biopsies from 2 patients with hypertriglyceridemia. The lesions had a granuloma annulare-like pattern at low magnification, the exceptional feature being their content of polarizable, needle-shaped crystals. These bore a strong resemblance to monosodium urate monohydrate and displayed negative birefringence under polarized light. In the case of each patient, an initial pathological diagnosis of gout was rendered, and the true nature of the lesions came to light only after clinicopathologic correlation. While it is clear that the chemical composition of these crystals requires further study, recognition of this microscopic variant of eruptive xanthomata should help to reduce errors in diagnosis.