Terbinafine is an allylamine antifungal commonly prescribed either topically or orally to treat dermatophyte infections. This case presents a photoallergic drug reaction secondary to oral terbinafine that may have been exacerbated by the accompanying topical terbinafine.

A 68-year-old woman was prescribed oral terbinafine in addition to topical terbinafine for a widespread intensely pruritic tinea incognita infection which had been mistakenly treated with topical corticosteroids for a prolonged duration. She had been applying topical terbinafine to affected areas for two weeks with symptomatic improvement noted over her abdomen and groin but minimal improvement over her arms, legs and chest. Routine bloods were reviewed and oral terbinafine was prescribed additionally in light of the widespread nature of her infection. Her only other regular medication was oral perindopril arginine for management of hypertension which she has been taking for approximately five years. Over the next seven days, she felt increasingly unwell, with fatigue and nausea. She also began to develop worsening erythema, oedema and eventually cutaneous pain over her upper and lower limbs and décolletage which had been treated with topical terbinafine. She also developed this rash over areas not exposed to topical terbinafine including the dorsal hands and her neck. Her face was unaffected. She had continued to swim outdoors each day wearing a swimsuit which covered her from mid upper arm to mid-thigh. She did not report any fevers, any mucosal involvement or any blistering. She was reviewed and found to have a violaceous and erythematous finely scaled rash with associated oedema in a clear photo-exposed distribution, with sparing on the regions covered by her swimsuit (Fig. 1). A full blood count, electrolyte/urea/creatinine, liver function tests, calcium/magnesium/phosphate and C-reactive protein were reviewed, and no issues were identified with normal liver function tests and eosinophils. Two punch biopsies were sent for H&E and showed a subacute spongiotic dermatitis and was consistent with a photoallergic drug rash. She was advised to cease the topical and oral terbinafine, minimise her sun exposure and was commenced on oral prednisolone 0.5 mg/ kg, a topical corticosteroid twice daily and oral cetirizine. She noted marked symptomatic improvement with these measures and her rash began to resolve over the following weeks, requiring no further topical or systemic treatment. She declined to have photopatch testing.

There have been sporadic case reports of terbinafine precipitating photosensitive skin rashes, including systemic lupus erythematosus [1], cutaneous lupus erythematosus [2], photoallergic [3], phototoxic [4], and photo-distributed acute generalised exanthematous pustulosis [5]. This case reiterates the importance of awareness of this rare complication. This case also raises the possibility that terbinafine applied topically may have exacerbated the photosensitive rash as our patient reported minimal improvement in the rash with the topical terbinafine in sun-exposed areas while noting significant improvement in areas not exposed to the sun.

Figure 1. 

Violaceous finely scaled rash with associated oedema affecting photo-exposed areas.