Dear Editor:

Hydroxychloroquine is an antimalarial drug, which is also extensively used in the treatment of dermatology and rheumatology. Its side effects, besides ocular toxicity, include gastrointestinal discomforts, such as nausea, vomiting, cramping and diarrhea1. Hydroxychloroquine can lead to hyperpigmentation on the skin, mucosa membrane, and nails; and to a white discoloration of blond, red, and light-brown hair;1 and in rare cases, it can cause hair loss1 and pruritus2. Side effects of the central nervous system include dizziness, headache, hyperexcitability, nervousness, insomnia, psychosis/depression, and reduced seizure threshold1. Although some kinds of the drugs, including anticholinergic, sedative-hypnotics, antidepressant and antianxiety, antiepileptic, analgesics, antiarrhythmic and statins, etc., have been reported with drug-induced hypomnesis, to our knowledge, no case of hydroxychloroquine-associated hypomnesis has been described before. Herein, we reported a man with reticular erythematous mucinosis (REM) who developed reversible hypomnesis after treated with hydroxychloroquine.

A 40-year-old Chinese male was referred with 1 year history of cutaneous lesion on his posterior chest, showing slow and progressive growth, causing occasional pain. The lesion didn't respond to antibiotics, such as penicillins or cephalosporins, or to systemic steroids, but mild response was noted to intra-lesional prednisolone. Cutaneous examination showed a clearly delimited reticulated erythematous plaque of 12×7 cm in the left back chest, with slight infiltration of the borders. Skin biopsy and pathology study showed abundant interstitial deposits of mucin in the dermis together with moderated perivascular and perifollicular lymphocytic infiltrate. After excluding secondary diseases, REM was diagnosed. The patient was then prescribed hydroxychloroquine 0.2 g, twice daily alone, which led to an excellent result after 2 months treatment, but the patient developed a progressive hypomnesis hereafter. He also noticed that the hypomnesis was milder when he took hydroxychloroquine 0.2 g daily than 0.2 g, twice daily; and the symptom would recover after stopping the medication for about 1 week, and recurred after taking it again. He recovered completely after stopping the medication.

REM, first described by Steigleder, is a rare cutaneous disease, characterized by persistent erythema in a reticular pattern and/or confluent erythematous papules and plaques, with a predilection of location on the central area of the chest or on the upper back; and rarely on the arms, face and abdominal region3-5. It predominantly afflicts middle-aged women3-5. The typical histopathology is interstitial deposits of mucin in the dermis. The pathogenesis remains unclear3,4.

Antimalarial drugs are the treatment of choice for REM3-5. Hydroxychloroquine, a derivative of chloroquine, is frequently used as the first-line treatment, and it always results in rapid improvement within about a month of starting the treatment; however, recurrence is also common5. The present patient responded well to hydroxychloroquine. Unfortunately, he had hypomnesis after administrated the drug. Based on the dosage-adverse effects relationship, we considered that hydroxychloroquine is responsible for the hypomnesis, but the mechanism is unclear.

Although such a condition is very rare and the present patient had finally recovered, practitioners should be aware of it as it may have a negative impact on patient's quality of life, and even lead severe problem.