An unusual cause for hyponatremia with seizures

A 50-year-old Asian Indian female with known hypertension presented with persistent vomiting but no other symptoms of meningism. Clinical examination and basic laboratory parameters were entirely normal except for significant hyponatremia. Further investigation was suggestive of the syndrome of inappropriate antidiuretic hormone (SIADH) secretion. Subsequently, despite steady correction of hyponatremia, the patient developed generalised seizures. Cerebrospinal fluid (CSF) analysis performed was inconclusive. Screening for a chronic meningitis underlying SIADH, yielded positive blood and CSF titres for venereal disease research laboratory (VDRL), which were confirmed by Treponema pallidum haemagglutination (TPHA). The patient was treated for neurosyphilis and made a complete recovery. Hyponatremia resolved and she had no further episodes of seizures. She was tested for HIV infection which was negative. On follow-up, she remained TPHA positive but VDRL titres became negative.