Abstract

In recent years, nicotinamide (also known as niacinamide) oral supplementation has been increasingly used for keratinocyte carcinoma prophylaxis in high-risk individuals. Nicotinamide, a water-soluble form of vitamin B3, has been shown in randomized clinical trials to significantly reduce incidence of actinic keratosis and keratinocyte carcinoma when taken chronically at a dose of 1,000-3,000 mg a day. Oral nicotinamide is generally well-tolerated but cutaneous adverse effects of pruritus, acanthosis nigricans, and transient rash have been reported. Here, we present a rare case of persistent psoriasiform eruption after starting nicotinamide supplementation that demonstrated eosinophilic interface dermatitis on repeat biopsies. The patient is an 85 year-old woman who presented for evaluation of well-demarcated, erythematous, coalescent papules and plaques with micaceous scale on the distal, extensor upper and lower extremities. These lesions developed four weeks following Mohs excision of a squamous cell carcinoma in-situ and initiation of oral nicotinamide, which the patient failed to disclose. Shave biopsy revealed vacuolar interface dermatitis with a lymphohistiocytic infiltrate and scattered eosinophils consistent with drug exanthem. Her eruptions initially improved with oral prednisone taper and high potency topical steroid but then flared. Repeat punch biopsy showed lichenoid dermatitis with numerous eosinophils with focal eosinophilic spongiosis and spongiform pustule. This prompted further inquiry of her medication history which uncovered her ongoing nicotinamide supplementation as the most likely culprit. The patient was advised to discontinue her oral nicotinamide and her eruptions gradually cleared. In conclusion, this is the first documented case to our knowledge of chronic psoriasiform interface dermatitis secondary to oral nicotinamide supplementation.

Financial Disclosure:
No current or relevant financial relationships exist.