Nervus intermedius neuralgia

Nervus intermedius neuralgia, or geniculate neuralgia, corresponds to a clinical manifestation of sudden paroxysms of excruciating otalgia which usually lasts a few seconds to a few minutes, involving the nervus intermedius (intermediate nerve of Wrisberg).

Epidemiology

Nervus intermedius neuralgia typically occurs in middle-aged women ¹. Although the exact incidence is unknown, it is considered far less common than trigeminal neuralgia ¹.

Clinical presentation

The clinical diagnostic criteria for nervus intermedius neuralgia are defined by the International Classification of Headache Disorders 3^rd edition (ICHD-3) as ²:

• at least three attacks of unilateral pain 
• the pain is located in the auditory canal, sometimes radiating to the parieto-occipital region
• the pain has at least three of the following four characteristics
  • recurring in paroxysmal attacks lasting from a few seconds to minutes
  • severe intensity
  • shooting, stabbing or sharp in quality
  • precipitated by stimulation of a trigger in the posterior wall of the auditory canal and/or periauricular region
• no clinically evident neurological deficit
• not better accounted for by another ICHD-3 diagnosis

The ICHD-3 further comments that disorders of lacrimation, salivation and/or taste sometimes accompany the pain of nervus intermedius neuralgia, and that the pain may result in secondary psychological effects and impairment to quality of life ².

Pathology

It is not certain what exactly causes nervus intermedius neuralgia ³. However, the leading hypothesis considers that the condition is caused by irritation of the nervus intermedius, most likely via compression from a blood vessel, similar to trigeminal neuralgia, glossopharyngeal neuralgia, and vagoglossopharyngeal neuralgia ^4,5. This theory is supported by the observation that many patients report benefits after vascular decompression ^4,5,8.

However, given that there are a number of other cranial nerves with afferents in the ear, it remains unclear whether all cases are due to irritation of nervus intermedius, or are actually due to irritation of other nearby cranial nerve afferents ^2,3. Indeed, many case reports describe decompressing multiple cranial nerves in order to attain symptom relief ³.

Additionally, there are other etiologies of this clinical syndrome:

• multiple sclerosis
• mass lesion in the cerebellopontine angle
• Ramsay Hunt syndrome, known as 'nervus intermedius neuropathy attributed to Herpes zoster' in the ICHD-3
• a possible familial syndrome that has an autosomal dominant or X-linked dominant pattern of inheritance ⁶

Radiographic features

The main role of imaging is to identify potential causes.

CT

CT is unable to visualize the nervus intermedius, and may only detect an obvious mass lesion ⁷.

MRI 

The nervus intermedius is only visible on 3T MRI, especially on heavily T2 weighted thin section images ⁷. Contrast should be administered to assess for abnormal enhancement of the nerve or surrounding structures ⁴. Furthermore, MRA is required to assess for a compressing ectatic vascular loop, most commonly on the root entry zone of the nervus intermedius-vestibulocochlear nerve complex ⁴.

Additionally, in one study, functional MRI was used to demonstrate that stimulation of the facial nerve in a patient with nervus intermedius neuralgia reproduced the otalgic symptoms and resulted in ipsilateral brainstem activation corresponding to the afferent distribution of the nervus intermedius ⁴. It is unclear if this technique has much potential for routine clinical utility.

Treatment and prognosis

Management can involve pharmacotherapy (e.g. carbamazepine) and/or neurosurgical intervention (either microvascular decompression or excision of the nervus intermedius and geniculate ganglion) ^3,4,8,9. In multiple case reports and case series, ‘excellent’ outcomes have been reported after neurosurgical intervention ^8,9.

History and etymology

Although the original description of nervus intermedius neuralgia is often attributed to James Ramsay Hunt (1872–1937), an American neurologist, who described a series of patients with Herpes zoster in 1937 ¹⁰, the first description was actually by American physicians L. Pierce Clark and Alfred S. Taylor in 1909 ¹¹.