Refractory SIAD Triggered by Herpes Zoster Ophthalmicus: Impact of Postherpetic Neuralgia on Hyponatremia Duration and the Role of Tolvaptan-A Case Report

An 86-year-old man developed syndrome of inappropriate antidiuresis (SIAD) following herpes zoster ophthalmicus (HZO). The patient presented with symptomatic hyponatremia and impaired consciousness. Hypertonic and isotonic saline infusions improved both parameters; however, oral sodium supplementation and fluid restriction alone failed to maintain normonatremia. Tolvaptan was added, resulting in temporary correction of sodium levels; however, SIAD relapsed after discontinuation. Ultimately, SIAD resolved with improvement in neuropathic pain. This case highlights a therapeutic strategy for symptomatic hyponatremia and the appropriate use of tolvaptan in refractory SIAD, and provides a review of HZO-induced SIAD, an uncommon but noteworthy clinical entity.