Abstract:

Objective To investigate the clinical characteristics and management strategies of antidepressant-induced syndrome of inappropriate antidiuretic hormone secretion (SIADH) in patients with comorbid parkinsonism and anxiety/depression, and to summarize clinical experience in the diagnosis and management of such comorbid conditions from an integrated neuropsychiatric perspective. Methods The clinical data of a patient with parkinsonism who developed severe hyponatremia after the antidepressant regimen was switched to venlafaxine were retrospectively reviewed. The case was analyzed in conjunction with the relevant literature, with a focus on pharmacological mechanisms, clinical manifestations, and management strategies. Results The patient was a 70-year-old man who had received long-term antidepressant treatment for anxiety and depression. After switching to venlafaxine, he developed severe hyponatremia (serum sodium, 126 mmol/L), manifested by worsening bilateral lower-extremity weakness, poor mental status, and dysarthria. These manifestations were difficult to distinguish from progression of Parkinson's disease and recurrence of depression. Laboratory findings were consistent with a diagnosis of SIADH. After discontinuation of venlafaxine and sodium supplementation, serum sodium levels returned to normal, accompanied by marked improvement in neuropsychiatric symptoms. A literature review identified 4 similar cases of comorbid conditions, all reported as individual case reports, with delayed diagnosis being a common feature. Conclusion Patients with comorbid parkinsonism and anxiety/depression are at substantial risk of developing SIADH when treated with serotonin and norepinephrine reuptake inhibitors (SNRIs) or selective serotonin reuptake inhibitors (SSRIs). When unexplained worsening of neuropsychiatric symptoms occurs in such patients, metabolic abnormalities such as hyponatremia should be ruled out first. Routine monitoring of serum sodium levels and multidisciplinary collaborative management are recommended.

Key words: depressive disorder, syndrome of inappropriate antidiuretic hormone secretion, hyponatremia, venlafaxine, parkinsonism, psychoneurological integration