Urgent considerations
See Differentials for more details
Meningitis
The meninges may become inflamed in response to viral, bacterial, or fungal infection, carcinomatosis, or neurosarcoidosis. The patient will typically be unwell, and clinical features may include photophobia, fever, stiff neck, headache, and rash (typically a non-blanching rash of meningococcal septicaemia). Cranial nerves III, V, VII, IX, X, and XII may be affected, and a neuropathy may present either in isolation or in combination. An urgent brain computed tomography (CT) is needed to exclude other urgent causes, followed by a lumbar puncture (LP) to obtain a sample of cerebrospinal fluid (CSF) for microscopy and culture.[110] Broad-spectrum antibiotics should be given presumptively if meningitis is suspected, ideally after blood cultures are collected.
Arteritic ischaemic optic neuropathy (giant cell arteritis)
Diagnosis should be considered in a patient 50 years or older who presents with new onset temporal headache, visual disturbances, or jaw or tongue claudication.[111] Approximately one third of patients will have symptoms of polymyalgia rheumatica, characterised by pain and stiffness in the head and neck and proximal upper and lower extremities. Constitutional symptoms including fatigue, weight loss, malaise, and fever also are common presenting symptoms.
These patients can develop rapid visual loss due to optic neuropathy that is preventable with timely use of corticosteroids. Screen with erythrocyte sedimentation rate (ESR) and/or C-reactive protein (CRP). If these are elevated, high-dose corticosteroids should be started and a temporal artery biopsy arranged to confirm the diagnosis.[112] Rarely patients may present with neuropathies of cranial nerves III, IV, or VI.[74] Patients should be evaluated by a specialist, ideally on the same working day if possible, and in all cases within three working days.[112]
Subarachnoid haemorrhage
This may follow rupture of a cerebral aneurysm or bleeding after a head injury. The patient presents with a sudden-onset severe headache or sudden altered consciousness, and there may be vomiting, neck stiffness, or seizures. An isolated dilated pupil may reflect rising intracranial pressure and herniation. A third, fourth, or sixth nerve palsy may be evident, and urgent CT/magnetic resonance imaging scan (MRI) brain is needed. If confirmed, an urgent neurosurgical consult is required.
If brain imaging is negative but the index of clinical suspicion for subarachnoid haemorrhage remains high, then a lumbar puncture looking for evidence of recent bleeding (xanthochromia) should be performed.[113]
Cerebral aneurysm
Patients with acquired, non-traumatic, isolated third nerve palsy with pupillary involvement should be evaluated for the presence of an unruptured intracranial aneurysm that may be compressing the third cranial nerve in the subarachnoid space. Initial evaluation with a cerebral or CT angiogram is recommended.
Uncal herniation
A new third nerve palsy with pupillary involvement can be a sign of impending uncal herniation. These patients demand rapid evaluation with a head CT. If neuroimaging cannot be obtained urgently and suspicion for herniation is high, presumptive treatment with hyperventilation and/or mannitol can be temporarily instituted. This may occur with increased intracranial pressure.
Intra-axial lesion
Acute onset of a trigeminal neuropathy, often accompanied by other neurological signs, may suggest a brainstem lesion such as pontine stroke or haemorrhage, or spinal cord pathology, such as cervical disc disease. Brain or cervical MRI as appropriate is recommended.[81]
Guillain-Barré syndrome and its variants
Acute immune demyelinating polyneuropathy (commonly referred to as Guillain-Barré syndrome) predominantly presents with limb weakness. Cranial motor involvement can also be seen. This may range from facial motor weakness, to oropharyngeal weakness (difficulty swallowing), to ophthalmoparesis. Some variants such as Miller-Fisher syndrome (ophthalmoplegia, ataxia and areflexia) and facial diplegia variant may manifest with predominant cranial motor dysfunction.[114][115]
Prompt investigation, such as CSF analysis, electrodiagnostic studies, and neuroimaging (MRI of neuraxis and/or peripheral nerve ultrasonography), is recommended.
Skull-base osteomyelitis
Neuropathy of nerve V, IX, X, or XII associated with otalgia, otorrhoea, hearing loss, and headaches, with or without fever, may herald a diagnosis of skull-base osteomyelitis. Patients should undergo head CT and MRI to assess for bony destruction and soft-tissue changes.
Herpes zoster ophthalmicus
Herpes zoster in the V1 distribution of the trigeminal nerve can cause keratitis, corneal scarring, and visual loss. Therefore, a prompt ophthalmological consult is warranted to prevent permanent damage.
Trauma
Head trauma that results in an isolated or multiple cranial nerve neuropathy needs urgent evaluation. Non-contrast thin-section head CT should be performed, with special attention to possible orbital, mid-face, mandibular, or skull-base fractures. Skull-base fracture may account for deficits in cranial nerves VII, IX, or X.
Ischaemic stroke (cerebral infarct)
It is critical to exclude a central cause of a seventh cranial nerve palsy of acute onset. Cortical or pontine strokes can often be recognised based on history and neurological exam findings, including sparing of the upper face (cortical) and presence of associated neurological deficits, such as contralateral limb weakness or altered mental status.
In the hyperacute setting, these findings should prompt immediate neuroimaging and assessment to determine whether the patient is a candidate for thrombolysis and/or mechanical thrombectomy.
Parapharyngeal space infection
Ninth, tenth, or twelfth nerve palsy in the setting of neck pain and fever may be due to a parapharyngeal space infection. Routine blood tests should be performed to include full blood count (FBC), CRP, and blood cultures. A neck CT with contrast will confirm the diagnosis.[116]
Medullary lesion
Lesions of the medulla can rarely result in isolated hypoglossal nerve palsy. They are more commonly associated with additional neurological findings and cranial nerve deficits. If one is suspected, assessment with prompt brain MRI is warranted.
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