Localized sarcoidosis in an old tattoo: Illustrating the principle of locus minoris resistentiae

A 33-year-old man with a five-year history of sarcoidosis, diagnosed by pathology of a hilar lymph node, presented with four weeks of arthralgias and new skin lesions. Prior to current presentation, his sarcoidosis was in remission without any active treatment. He was referred to dermatology for further evaluation of his skin lesions. Dermatology consultation revealed firm papules involving multiple tattoos on the patient’s neck, arm, and wrist (Figure 1). All tattoos had been placed over ten years prior to this visit, also antecedent to first diagnosis of sarcoidosis. The patient was also found to have tender nodules with overlying erythema on the lower legs thought to be consistent with erythema nodosum (EN). Given the constellation of EN, arthralgias, and the patient’s known history of sarcoidosis, he was diagnosed with likely Lofgren syndrome, and a chest X-ray obtained confirmed hilar lymphadenopathy. A biopsy of a lesion on the forearm revealed dermal granulomatous dermatitis with peripheral lymphocytes and scattered eosinophils, consistent with cutaneous sarcoidosis within a tattoo (Figure 2). A granulomatous response to tattoo ink could not be ruled out, however thought unlikely given the clinical context of this new skin eruption. He was started on low dose prednisone, which resulted in improvement in his arthralgias, however his skin lesions persisted. He was initiated on topical betamethasone for the skin lesions, and in follow-up was found to have improved cutaneous disease. This case of cutaneous sarcoidosis in an old tattoo illustrates the principle of locus minoris resistentiae (LMR), the phenomenon of skin lesions presenting at sites of reduced integrity. With the onset of Lofgren syndrome in this patient, it was notable that the only cutaneous lesions outside of EN were found in old tattoos, and normal skin remained uninvolved.