What investigations are needed for a patient presenting with sixth nerve palsy?

From the Guidelines

Patients presenting with sixth nerve palsy require a comprehensive workup to determine the underlying cause, and initial investigations should include a complete blood count, erythrocyte sedimentation rate, C-reactive protein, and blood glucose levels to screen for inflammatory conditions and diabetes, as well as neuroimaging with MRI brain and orbits with contrast as the preferred modality 1. The workup for sixth nerve palsy involves several key components, including:

• Laboratory tests: complete blood count, erythrocyte sedimentation rate, C-reactive protein, and blood glucose levels to screen for inflammatory conditions and diabetes 1
• Vascular risk factor assessment: lipid profile and blood pressure monitoring 1
• Neuroimaging: MRI brain and orbits with contrast as the preferred modality to evaluate for structural lesions such as tumors, aneurysms, or demyelination; CT may be used if MRI is contraindicated 1
• Additional targeted tests: thyroid function tests, autoimmune markers (ANA, ANCA), and specific infectious disease testing based on clinical suspicion 1
• Cerebral angiography: may be necessary if vascular abnormalities are suspected 1
• Lumbar puncture: should be considered to rule out infectious or inflammatory causes, particularly if there are signs of increased intracranial pressure or meningeal irritation 1 The urgency of these investigations depends on the clinical presentation, with complete, painful, or pupil-involving palsies requiring more immediate evaluation due to their association with potentially serious underlying pathologies 1. Some key points to consider in the workup and management of sixth nerve palsy include:
• The importance of neuroimaging in all young patients or in any patient manifesting other cranial neuropathies, other neurologic change or elevated IOP, or signs of elevated intracranial pressure, or if there are no compelling vasculopathic risk factors 1
• The need for referral to a neuro-ophthalmologist or other subspecialist if the primary diagnosis is uncertain or for directed treatment 1
• The goal of treatment is to eliminate diplopia in the primary position and to create a reasonable field of single binocular vision, with patients likely to continue to have diplopia in more extreme lateral gaze due to the underlying neurological deficit 1

From the Research

Investigations for Sixth Nerve Palsy

The following investigations are needed for a patient presenting with sixth nerve palsy:

• MRI: To determine the frequency of a causative lesion, such as a tumour or tumour-like lesion, or presumed vasculopathy 2
• Ocular coherence tomography (OCT): To diagnose optic neuritis and multiple sclerosis, especially in children 3
• Neuroimaging studies: To diagnose intracranial aneurysms, which can present with isolated sixth nerve palsy 4
• Blood tests: To rule out underlying conditions such as multiple myeloma or plasmacytoma 5
• Cerebrospinal fluid (CSF) analysis: To diagnose conditions such as multiple sclerosis or infections 6
• CT head: To rule out other causes of sixth nerve palsy, such as trauma or mass lesions 6

Specific Considerations

• If the patient has a history of vasculopathy, follow-up MRI may not be necessary if the symptoms regress spontaneously 2
• Children with sixth nerve palsy should be evaluated for multiple sclerosis, and clinicians should have a high index of suspicion for early diagnosis and treatment 3
• Sixth nerve palsy can be a presenting symptom of cerebral aneurysms, and neuroimaging studies should be considered in these cases 4