Hemifacial Spasm

Hemifacial spasm is unilateral involuntary, intermittent contractions of muscles supplied by the facial nerve.

• Incidence 1 per 100,000; onset in middle to late age, more in women and Asian populations.

• Cause: vascular compression of the facial nerve at the root exit zone (anterior inferior cerebellar artery, posterior inferior cerebellar artery) in most; also tumour, aneurysm, arteriovenous malformation, demyelination, post Bell palsy.

• Ephaptic transmission and nuclear hyperexcitability explain synkinesis and lateral spread.

• Twitching of orbicularis oculi spreading to cheek, mouth, platysma on one side, persisting during sleep in severe cases.

• Prolonged tonic contraction closing the eye, mouth pulled laterally.

• Worse with stress, fatigue, facial movement; hearing click (stapedius).

• No facial weakness (initially), differentiating from facial myokymia and blepharospasm.

• Clinical.

• MRI brain with high resolution T2 (CISS/FIESTA) and MR angiography to show neurovascular conflict, exclude tumour, aneurysm.

• EMG: lateral spread response (abnormal muscle response) on stimulation of one branch of the facial nerve.

• Exclude blepharospasm (bilateral), facial tic, seizures, myokymia.

• Botulinum toxin injection (onabotulinumtoxinA 1.25 to 2.5 units per site, total 20 to 50 units) every 3 to 4 months, effective in 85 to 95%.

• Oral drugs have limited efficacy: carbamazepine 100 to 400 mg twice daily, oxcarbazepine, gabapentin, clonazepam 0.5 to 1 mg, baclofen.

• Microvascular decompression (Jannetta procedure) for failure of botulinum toxin or patient preference: cure in 85 to 90%; risks include hearing loss (1 to 3%), facial weakness, CSF leak.

• Review and re-injection schedule; reassure about benign nature.