Cutaneous sarcoidosis: an intriguing model of immune dysregulation

Sarcoidosis is a systemic granulomatous disease characterized by the presence of non-caseating granulomas. Its etiology remains obscure. A plausible hypothesis suggests that a complex interplay of host factors, infectious processes, and non-infectious environmental factors, matched with a susceptible genetic background, results in a pathway that leads to systemic granulomatous inflammation. Although presentations of sarcoidosis vary enormously, multi-organ involvement is a common feature. Cutaneous involvement occurs in about 25% of patients with protean manifestations and variable prognoses. Skin manifestations are divided into specific lesions with histopathologically evident non-caseating granulomas and nonspecific lesions arising from a reactive process that does not form granulomas. A peculiar form of cutaneous sarcoidosis is represented by sarcoidal lesions at sites of trauma that has caused scarring. The pathogenesis of scar sarcoidosis remains unknown. Scar sarcoidosis is also associated with herpes zoster infection, surgery, and tattooing. Such heterogeneous events, along with those at the sites of chronic lymphedema, thermal burns, radiation dermatitis, and vaccinations, occur on areas of vulnerable skin labeled "immunocompromised districts". Numerous options are available for the treatment of cutaneous sarcoidosis. Although corticosteroids remain the treatment of choice for initial systemic therapy, other nonsteroidal agents have proven effective and therefore useful for long-term management. Tumor necrosis factor-α antagonists such as infliximab may have a role in the treatment of cutaneous sarcoidosis, especially in refractory cases that are resistant to standard regimens. Elucidation of the relationship of sarcoidal granulomas with malignancy and immunity may facilitate a better understanding of some pathomechanisms operating in neoplastic and immunity-related disorders.