[A patient with thyroid carcinoma who developed consciousness disturbance during acyclovir administration for herpes...

A 69-year-old man developed confusion and disorientation, following intravenous administration of acyclovir for herpes zoster at the right C5 area. His consciousness was disturbed four days after the beginning of acyclovir therapy (daily dose: 500 mg, every 12 h), and the symptoms resolved two days after cessation of acyclovir. Neuroradiological examination revealed no intracranial abnormality, and the routine CSF examination was within the normal range of values except for a mild elevation of IgG (7.4 mg/dl). An electroencephalogram showed diffuse slow activities without paroxysmal waves on admission, but the findings of electroencephalograms were gradually normalized in parallel with the recovery of consciousness. Fever, signs of meningeal irritation, involuntary movement or renal dysfunction were not observed during the course of illness. Although the serum concentration of acyclovir was not elevated, we considered the adverse effects of acyclovir had resulted in his consciousness disturbance. Acyclovir is greatly useful for herpes simplex and varicella-zoster virus infections, and its complications are extremely rare. However, several reports described various neuropsychiatric side effects in patients receiving acyclovir. Most of such cases had an association with severe renal failure or malignant tumor; actually, an intense malignancy surveillance over our case revealed thyrogenic papillary adenocarcinoma without metastasis. The excretion of acyclovir is mainly through the kidney, so that the neurotoxicity of acyclovir in cases with renal insufficiency stems from its excessive accumulation in the body. In malignancy complicated patients, on the other hand, some authors surmised about the influences from the co-use of other neurotoxic drugs or radiation therapy, but reasons for such conditions remain obscure. The neuropsychiatric manifestation caused by acyclovir is an entity distinguishable from viral encephalitis, and a careful surveillance for malignancy is required in such cases.