Neurology: Headaches in optometric practice part 2 – trigeminal neuralgia

A 46-year-old patient had been suffering intermittent severe headaches for six years and was under the care of her general practitioner. The headaches would occur at least weekly and could last between a few hours up to several days.

There was no visual aura, although her practitioner had been treating her for migraines (in error as it turned out). Her GP suggested that she had an eye test before he would consider treating her for cluster headaches.

On her first visit to the practice, careful questioning of the nature of the headaches revealed that she had been suffering a very sharp boring pain behind the right eye and, on many occasions, pain from the right lower teeth. She had tried a host of pain killers (Imigran, paracetamol and ibuprofen) to no avail. There was no general health or refractive issues and no family history of migraines.

Examination was unremarkable with no fundus or anterior segment abnormalities and the intraocular pressures were within normal limits.

Listening to the patient’s symptoms (boring pain and tooth involvement) sounded more like cranial nerve neuralgia and my suggestion was to see a dentist first to rule out any hypersensitive dental nerve, root or gum problem or tooth decay. If all this was negative, then referral to a neurologist or oral and maxillofacial consultant seemed the appropriate next step.

Diagnosis

Six years from her first episode of headache she was seen by the oral and maxillofacial consultant who carried out an MRI scan which ruled out any brainstem lesions or vascular abnormalities. Incidentally, the scan revealed sinus blockage but not on the side of the headache. A diagnosis of atypical trigeminal neuralgia was made and she was prescribed oral gabapentin 300mg three times daily.

Four months later she has been headache and pain free and she will be continuing with the treatment for the foreseeable future.

Cluster headaches

Cluster headaches are rare, very often misdiagnosed and dissimilar to migraine headaches. They are usually located behind one eye and pain is persistent and described as an explosive, boring or searing pain. The headaches may be so intense that patients pace and rock or rub to get relief and sometimes bang their heads against the wall to ease the pain. Associated with the headache, there may be ipsilateral symptoms of cranial autonomic activation. The unilateral pain around one eye together with watering of the eye, rhinorrhoea, nasal congestion, eyelid swelling, facial sweating and conjunctival injection on the ipsilateral side. A pseudo-Horner’s syndrome (miosis and ptosis) may occur. The very severe headache lasts for between 15 minutes to three hours, may be orbital, supra orbital or temporal, and tends to occur at night. This suggests involvement of the hypothalamus, the main regulator of circadian cycle.

In the UK there are roughly 90,000 sufferers with three to four times greater prevalence in males. Cluster headaches can start at any age but are most likely between the ages of 20 and 40 years. Alcohol is a potent trigger factor for cluster headaches as are vasodilators such as histamines and nitroglycerine. Disruption to sleep can also trigger cluster headaches and, in some patients, heat and exercise are precipitants. Inheritance is thought to be autosomal dominance type. Figure 1 summarises the underlying pathophysiology.

 Trigeminal neuralgia

Idiopathic trigeminal neuralgia describes a stabbing, shooting and ‘electric shock-like’ face pain in the areas supplied by the trigeminal nerve. These include the cheeks, jaw, teeth, gums and lips (served by the maxillary V2 and mandibular V3 nerves) and, less often, the area around the eye and the forehead supplied by the ophthalmic (V1) nerve. The pain can be spontaneous or triggered by stimuli such as light touch, cold air, chewing, talking, facial movement, teeth brushing or emotional distress. Trigger zones can be as small as 1-2mm and usually centred around the nose and lips. Attacks are thought to be due to direct damage to the nerve leading to focal demyelination and vascular insult. Pain is usually on one side of the face, but in 5 to 10 percent of cases pain is bilateral though not simultaneous.

In 60% of cases pain radiates from the corner of the mouth to the edge of the jaw (V3), in 30% pain starts from the top of the lip to the eye and the eyebrow sparing the orbit  (V2) and in less than 10% of cases the pain involves the ophthalmic branch of the facial nerve. Prevalence in the UK is 150 per 1 million and females are 1.5 times more likely to suffer than men. Most cases begin after the age of 40.

Pain commences with a sensation of electrical shocks in the affected area and crescendos in less than 20 seconds to excruciating discomfort. Within seconds this fades and gives way to a burning ache lasting seconds to minutes. Pain does abate between attacks even when they are frequent and severe. Attacks may provoke patients to wince or make aversive head movements (tic douloureux) to relieve pain.

Typical trigeminal neuralgia has five cardinal features:

• Paroxysmal facial pain (excruciating)

• Pain on provocation (light touch, chewing or shaving)

• Unilateral

• Confined to the trigeminal territory

• On sensory testing with pin prick there is absence of sensory loss

Atypical trigeminal neuralgia is characterised by longer periods of unprovoked unilateral, constant and severe aching, boring and burning pain superimposed with paroxysms of typical trigeminal neuralgia. It is thought that atypical trigeminal neuralgia is due to vascular compression of the trigeminal nerve.

Causes

Some 5% of cases are caused by neoplasms pressing on the trigeminal nerve, while another 5%, particularly in younger patients, are due to multiple sclerosis and in this case pain may be bilateral. The main cause of trigeminal neuralgia is vascular compression of the trigeminal nerve root, particularly by the superior cerebellar artery against the microvasculature of the trigeminal nerve near its connection with the pons. Compression may also be from the basilar artery and smaller arteries and veins. Recent research suggests that any of these influences causes a breakdown in the myelin sheath of the nerve leading to disruption of the normal signal and causing erratic and hyperactive functioning of the nerve as a response to even the slightest stimulation. Myelin disruption also hinders the nerve’s ability to shut off the pain signal after the stimulation ends.

Treatment

The first line of treatment for trigeminal neuralgia is an anti-epileptic drug (such as carbamazepine). Secondary approaches may include gabapentin, pregabalin, baclofen (a muscle relaxant), phenytoin, oxcarbazepine, lamotrigine and sodium valporate. Antidepressants, such as amitriptyline and duloxetine, are also effective. Opiates, such as morphine and oxycodone, help with neurotrophic pain. The surgical treatment favoured by most neurologists is microvascular decompression whereby a padding is placed between the offending vessel and the trigeminal nerve. Precutaneous procedures involve injecting glycerol or inflating a balloon around the Gasserian ganglion or applying heat to the Gasserian ganglion and, in turn, disrupting the pain signals. Side effects of these procedures to slight or permanent numbness to part of the face.

Anatomy

To fully understand the mechanism of trigeminal neuralgia it is best to go back to basic anatomy (Figure 2). The left and right vertebral arteries join at the level of the medulla to form the basilar artery (BA) which traverses to the top of the pons where it splits into the right and left posterior cerebral arteries (PCA). Before this, at the base of the pons, the anterior inferior cerebellar artery (AICA) branches to supply the anterolateral part of the cerebellum and there are also small pontine arteries that fan from the BA. Approaching the middle of the pons, and superior to the trigeminal nerve, is the superior cerebellar artery (SCA) supplying the upper surface of the cerebellum. The close proximity of the SCA makes it a likely cause of compression or pulsation leading to focal demyelination of the trigeminal nerve. Smaller pontine arteries (PA) may also aggravate the nerve. Remember acronym ‘ASP’ (AICA-SCA-PCA) for the basilar artery branches.

Also at the pons, below the trigeminal nerve, are the 7th and 8th cranial nerves (facial and vestibulocochlear) and so an acoustic neuroma could impede on the trigeminal nerve leading to compression and neuralgia as well as facial palsy and hearing loss (Figure 3). Similarly, demyelination at the level of the pons could lead to similar symptoms.

Conclusion

It is important for optometrists to understand the different types of unilateral head pains and I hope that providing the mechanisms behind the headaches will ensure that logical thought processes are applied in deciphering the pain. Thanks to all the patients who have kindly provided permission to discuss their cases.

Read more

Headaches in optometric practice part 1 – migraine

Kirit Patel works in independent practice in Radlett, Hertfordshire