Cold-associated perniosis of the thighs histopathologically mimicking lupus. Six observations.

Background: Equestrian cold panniculitis has been described since 1980 in horse riders or in stable employees. Histological aspect is underdescribed.

Patients And Methods: We describe clinical and histological features of six horse riding or stable employees patients presenting with upper lateral thigh lesions during the winter months between 2014 and 2016 in our dermatological department.

Results: Six horse riding or stable employees ladies without any known disease presented with similar symptoms. They had urticarial or violaceous, slightly pruritic, sometimes necrotic lesions of the upper lateral thighs. Clinically, equestrian cold panniculitis, insect bite or a caustic dermatitis was suspected. Four of these patients had a cutaneous biopsy. They all showed a similar histological appearance resembling lupus erythematosus, combining dermo-epidermal lesions, with foci of interface dermatitis, an abundant dermal lymphocytic infiltrate and a dermal mucinosis. Hypodermal infiltration was present on samples including subcutis. Laboratory workup for systemic disease was unremarkable for two patients and not performed for the four others, having no other clinical sign of lupus. All patients improved rapidly with very high potent topical steroids.

Conclusion: Cold-associated perniosis of the thighs should be considered whenever a histopathological appearance of lupus is associated with lesions of the upper lateral thighs in patients practicing horse riding. This disease belongs to the spectrum of miscellaneous cold-induced dermatoses in which histopathological lesions identical to lupus can be encountered.