Reversible central neural hyperexcitability: an electroencephalographic clue to hypocalcaemia

Abstract

A 23-year-old male patient presented with cognitive decline and seizures. Examination revealed Chvostek's and Trousseau's signs. Investigations revealed hypocalcaemia, hyperphosphatemia and normal intact parathyroid hormone levels. Imaging showed calcifications in bilateral basal ganglia, thalamus and dentate nuclei. Interictal electroencephalogram showed theta range slowing of background activity and bilateral temporo-occipital, irregular, sharp and slow wave discharges, which accentuated during hyperventilation, photic stimulation and eye closure. Appearance of epileptiform discharges after eye closure, hyperventilation and photic stimulation may suggest presence of central neural hyperexcitability due to hypocalcaemia. These features may be an equivalent of peripheral neuromuscular hyperexcitability (Chvostek's and Trousseau's signs) that occurs in hypocalcaemia. The clinical and electroencephalographic features completely reversed with correction of serum calcium without antiepileptic medications. It is important for clinicians to recognise these reversible changes, as it can help to avoid misdiagnosis and long-term administration of antiepileptic becomes unnecessary.

Keywords: clinical neurophysiology; epilepsy and seizures.

Figure 1

Electroencephalogram recording in bipolar montage (10/20 system) shows (A) hyperventilation induced sharp and slow wave discharges over bilateral temporo-occipital region, (B) photic stimulation induced sharp and slow wave discharges over bilateral temporo-occipital region and (C) irregular sharp and wave discharges occurring on eye closure. Recorded at 1 s×7.5 µV/mm.

Figure 2

CT brain plain image shows calcification in bilateral basal ganglia, thalamus and subcortical white matter.

Figure 3

Electroencephalogram recording in bipolar montage (10/20 system) shows normal background activity on (A) hyperventilation and (B) after eye closure. Recorded at 1 s×7.5 µV/mm.