Interchanging Autoimmunity - Lupus Mastitis Coexisting with Systemic Polyarteritis Nodosa.

Lupus mastitis is an uncommon presentation of lupus erythematosus profundus (LE profundus), characterized by inflammation of the subcutaneous fat. LE profundus occurring as initial manifestation of LE is rare. We report a case where the patient presented with lupus mastitis and years later, she developed disseminated discoid LE (DLE) and polyarteritis nodosa (PAN). PAN and DLE are connective tissue diseases with different etiologies, clinical, immunological, and histopathological features. One connective tissue disease evolving into another is rare, and the reasons remain unexplained. This woman had histopathologically proven DLE and lupus mastitis with a negative antinuclear antibody profile. She satisfied the American College of Rheumatology criteria for PAN.