Granular C3 dermatosis—A report of two cases and a mini‐review of literature

Abstract Granular C3 dermatosis (GCD) is characterized by bullous, erythematous, and eczematous skin lesions similar to dermatitis herpetiformis, and granular deposition of complement C3 and C5b‐9 along the epidermal basement membrane zone (BMZ) by direct immunofluorescence (IF). Here, we present two cases of GCD with different clinical features. Case 1, a 49‐year‐old man, showed pruritic blisters and erythema of the extremities. Case 2, a 53‐year‐old woman, showed severely pruritic papules, erythema, and erosions on the entire body with scattered blisters, mainly on the lower extremities. Both patients showed mild eosinophilia on blood tests, subepidermal blisters and prominent eosinophilic infiltration in the upper dermis on histopathological examination, and granular BMZ deposition of C3, but not of immunoglobulins or other complement components, on direct IF. No circulating autoantibodies were detected on enzyme‐linked immunosorbent assays, chemiluminescent enzyme immunoassays, indirect IF using 1 mol/L NaCl‐split normal human skin, or immunoblotting. Diagnosis of GCD was made in both cases. Case 1 was successfully treated with topical steroids, oral minocycline, and nicotinamide without any recurrence of symptoms. Case 2 was treated with oral steroids and showed remarkable improvement, although mild pruritic papules remained. We reviewed 30 reported GCD cases, including the two cases presented here, since Hashimoto et al. first described GCD in 2016. GCD should be more widely recognized, and further accumulation and validation of cases are required.