Metformin-induced photocontact dermatitis in a 67-year-old male: A case report

Abstract

Introduction Metformin is one of the most commonly used drugs in the field of medicine. It is an antihyperglycemic agent of the biguanide class. It decreases glucose levels primarily by decreasing hepatic glucose production and by increasing insulin action in muscle and fat.1 Metformin has a long-standing evidence base for efficacy and safety, is inexpensive, and may reduce risk of cardiovascular events and death.2 Thus, it is the mainstay in the initial treatment of type 2 diabetes mellitus (T2DM). Like any other drug, metformin is not without side effects. Its common side effects, which occur in up to 20% of patients, include diarrhea, abdominal discomfort, nausea, metallic taste and anorexia.1 Metformin allergy is rare. There is no current literature that convincingly implicate metformin Case Report Philippine Journal of Internal Medicine as the direct cause of allergic reactions. Vasculitis and psoriasisiform drug erruptions have been reported, wherein the patients usually develop a rash within a few days of metformin administration and the skin lesions disappear after stopping the drug, however, no causal relationship was established.3,4 We present a case of a patient who had metformin-associated photocontact dermatitis. Case Presensation This is a case of a 67-year-old male who presented with pruritic erythematous, scaly and desquamating lesions in sun exposed areas of the skin, which were noted to erupt about four months prior to consult. There was no associated fever or other constitutional signs and symptoms. The patient had no history of skin trauma, nor had any exposure to potential skin irritants such as liniments and creams. He has no personal history of atopy however family history was not clearly established. The patient drives a motorcycle as his form of livelihood, which allows him to be directly exposed to sunlight almost daily. The patient was diagnosed with T2DM four months prior to consult and was started on metformin 500mg tablet, taken The PHILIPPINE JOURNAL OF INTERNAL MEDICINE is a peer reviewed journal and a copyrighted publication of the Philippine College of Physicians Volume 57 Number 1 April-June, 2019 103 Introduction: Photocontact dermatitis is a type IV delayed hypersensitivity response to an allergen that is activated by radiation energy. Its incidence is uncertain and only a small number of drugs causing such reaction have been studied. This is a case of a 67-year-old filipino male, diabetic, who presented with scaly, erythematous, and hyperpigmented plaques with areas of desquamation and erosions on sun-exposed areas of the skin after taking metformin. Case: Four months prior to consult, the patient was diagnosed with type 2 diabetes mellitus and was started on metformin therapy. Days later, he started noticing scaly, erythematous and hyperpigmented plaques with areas of desquamation and erosions on sun-exposed areas, namely the upper and lower extremities, posterior neck, and forehead. There was notable sparing of areas that are usually covered with clothing such as the torso, inguina and both thighs. There were also no lesions on the scalp, palmar aspect of the hands and plantar surface of the feet. Skin biopsy was considered but was not done per patient’s preference. After discontinuation of metformin and avoidance from sun exposure, the skin lesions gradually improved. Conclusion: Metformin is rarely associated with adverse skin reactions. The diagnosis of photocontact dermatitis as a side effect of metformin needs to be considered as a differential diagnosis in patients who present with skin rashes, especially in sun-exposed areas. It is recommended that there should be a high-index of suspicion for adverse drug reactions in such patients. This would reduce medical errors and medical cost and would result to prompt initiation of appropriate treatment.