A 66-year-old woman receiving pembrolizumab for metastatic melanoma presented with tender red nodules on her shins and forearms. Biopsy was consistent with erythema nodosum (EN). The eruption responded to oral minocycline and potent topical steroids. Subsequent investigations detected bihilar lymphadenopathy, biopsied as granulomatous lymphadenitis, confirming the diagnosis of pembrolizumab-associated sarcoidosis. Pembrolizumab was stopped for two cycles and was restarted without recrudescence of EN or bihilar lymphadenopathy. Immunotherapy-associated sarcoidosis is a rare but recognized adverse event related to therapy with immune checkpoint inhibitors. EN is an uncommon manifestation of immunotherapy-induced sarcoidosis. New-onset bihilar lymphadenopathy in the context of immunotherapy requires prompt histological evaluation to differentiate between immunotherapy-associated sarcoidosis and metastatic progression. We review the literature related to immunotherapy-associated EN.
Keywords: erythema nodosum; immunotherapy; melanoma; pembrolizumab; sarcoidosis.
Pembrolizumab (trade name Keytruda®) is a type of immune therapy that stimulates the body's immune system to fight cancer cells. This immune therapy can cause a variety of rashes. In this article, we describe a patient who developed a red lumpy rash on her limbs that is not commonly described with pembrolizumab. A woman was diagnosed with advanced melanoma and was treated with pembrolizumab. She developed a red lumpy rash on her arms and legs, and a biopsy showed signs of a condition called erythema nodosum. Treatment with an antibiotic tablet and strong steroid ointment were helpful. Scans of her chest showed signs of sarcoidosis in her lungs, which can be associated with erythema nodosum. Pembrolizumab was stopped, and both the rash and lung sarcoidosis stayed away when it was restarted. This type of rash has rarely been described with this kind of immune therapy, and it can be a sign of lung involvement.