Differential diagnosis of posterior reversible encephalopathy syndrome and acyclovir neurotoxicity in children: A literature review of acyclovir neurotoxicity

Background Acyclovir (ACV), an antiviral drug commonly used in children, is associated with neuro- and nephron-toxicity. However, ACV neurotoxicity is mainly reported in adults and rare in children. Herein, we report the case of a boy with impaired consciousness following ACV treatment, posing challenges in differentiating posterior reversible encephalopathy syndrome (PRES) from ACV neurotoxicity. Additionally, we reviewed existing literature on ACV neurotoxicity. Case presentation A healthy 10-year-old boy developed severe headache and intermittent restlessness and was diagnosed with mild encephalitis/encephalopathy showing a reversible splenial lesion on magnetic resonance imaging (MRI). Since herpes simplex encephalitis could not be ruled out, ACV was initially administered. The patient later developed renal dysfunction, hypertension, and conscious disturbance. With a high serum ACV level of 14.3 μg/mL (reference; 0.4–2.0 μg/mL), we suspected PRES or ACV neurotoxicity. Upon discontinuation of ACV and starting antihypertensive therapy, the patient’s consciousness improved, leading to discharge without sequelae. In 14 pediatric cases with ACV neurotoxicity, including our case, the median age at onset was 10 years (range, 0–17 years), with renal dysfunction and high doses of ACV posing risk similar to adult cases. The mean time from ACV discontinuation to complete recovery was 5.6 ± 3.6 days, and the patients’ prognosis was good. Conclusions When a patient develops neurological symptoms during ACV treatment, considering the simultaneous occurrence of ACV neurotoxicity and PRES is crucial, including measuring their blood pressure, renal function, ACV levels, and MRI. Additionally, dosage should be adjusted based on ACV concentration in blood.