SIADH with Severe Hyponatremia in an Elderly Man with Herpes Zoster Infection: A Causal or Casual Association?

Syndrome of inappropriate antidiuretic hormone (SIADH) secretion is the most common cause of hypotonic hyponatremia in hospitalized patients. An elderly man with severe symptomatic hyponatremia (109 mEq/L) was diagnosed with SIADH that was likely secondary to large cutaneous herpes zoster (HZ) infection. Hypertonic saline and tolvaptan improved the patient's sodium levels and clinical condition. A one month after discharge, tolvaptan was withdrawn, due to inadequate prescription criteria, after which hyponatremia relapsed several times and was properly treated; eventually fever and sopor occurred and the patient died. SIADH secondary to HZ may induce life-threatening and long-lasting hyponatremia, which requires a prompt diagnosis and treatment.