What causes muscle twitching on the left side of the head?

Muscle Twitching Left Side of Head

Muscle twitching on the left side of the head is most likely hemifacial spasm, an involuntary contraction of muscles innervated by the facial nerve (cranial nerve VII), typically caused by vascular compression at the nerve's root exit zone from the brainstem. 1, 2

Primary Diagnosis: Hemifacial Spasm

Hemifacial spasm presents as rapid, involuntary, unilateral muscle contractions affecting one side of the face in the distribution of the seventh cranial nerve. 1 The condition is characterized by:

• Irregular clonic or tonic movements of facial muscles on one side 2
• Typically begins around the eye (orbicularis oculi) and spreads to involve the mouth (orbicularis oris) and sometimes the platysma muscle 3
• Can produce head-nodding or tremor-like movements in severe cases 1

Underlying Causes to Consider

Most Common: Vascular Compression (62% of cases)

• Primary or idiopathic hemifacial spasm results from vascular loop compression at the facial nerve root exit zone from the brainstem 2
• Tortuous vertebrobasilar system can compress both the facial nerve and adjacent structures 3

Secondary Causes (19% of cases)

• Previous Bell's palsy (11% of hemifacial spasm cases) 2
• Facial nerve injury (6% of cases) 2
• Demyelinating disease or brain vascular insults 2

Mimickers Requiring Different Management (18% of cases)

• Psychogenic movements, tics, dystonia, myoclonus, or hemimasticatory spasm can present similarly 2

Diagnostic Approach

Clinical Examination

• Observe the pattern of muscle contractions: hemifacial spasm is unilateral, irregular, and follows the facial nerve distribution 2
• Check for associated cranial nerve abnormalities that suggest structural lesions 4
• Assess for mild facial palsy on the affected side, which may coexist 3

Neuroimaging is Mandatory

• MRI of the head with and without contrast including high-resolution T2-weighted images of the cranial nerves is the preferred imaging modality to evaluate for vascular compression, brain stem lesions, and cranial nerve abnormalities 4
• MRA or CTA should be performed to assess for vascular compression from tortuous vessels 4, 3

Electromyography

• EMG can provide evidence of facial nerve damage and confirm the diagnosis 5

Triggers and Exacerbating Factors

• Vasodilators (such as nitrates) can promptly trigger or worsen muscle twitching in hemifacial spasm 6
• Migraine attacks may trigger hemifacial spasm in predisposed patients through central hyperexcitability or vessel dilation compressing the facial nerve 5

Critical Pitfalls to Avoid

• Do not assume benign etiology without neuroimaging—secondary causes including tumors, demyelination, and vascular malformations must be excluded 2
• Do not overlook atypical features such as bilateral involvement, associated neurological deficits, or involvement of other cranial nerves, which suggest alternative diagnoses 4, 2
• Do not miss the 18% of cases that are mimickers requiring entirely different management approaches 2
• Do not attribute symptoms to stress or anxiety without proper workup—psychogenic movements are a diagnosis of exclusion 2

Treatment Considerations After Diagnosis

• Botulinum toxin injections are the primary treatment for idiopathic hemifacial spasm 6
• Microvascular decompression surgery is definitive treatment for vascular compression cases 2
• Avoid vasodilating medications that can exacerbate symptoms 6