Atypical Facial Neuralgias
Neuralgias are syndromes characterized by intermittent attacks of sharp and paroxysmal pain along the course of a nerve. The neuralgias involving the face are often misdiagnosed and seen initially by the dentist or otolaryngologist. Therefore treatment is often delayed and patients may unnecessarily suffer from neuropathic pain until someone correctly recognizes the signs and refers the patient to a neurologist. The authors describe some of the atypical and lesser-known neuralgias of the face.
Neuropathic pain originating in the back of the head along the distribution of the occipital nerves is called occipital neuralgia (see Figure 1). The greater occipital nerve, which originates from the posterior root of the second cervical nerve in the neck, is the most common nerve to be involved. The lesser occipital nerve, arising from the posterior branch of the third spinal nerve in the cervical spine and situated behind the mastoid, is less commonly affected.
Occipital neuralgia is most commonly idiopathic in that no causative factor can be identified. It can sometimes be secondary to injury to the nerve (e.g. direct trauma to the occipital nerves from a whiplash hyperextension injuries), compression of the nerve (between atlas and axis), or the upper cervical roots from arthritic changes in the spine (rheumatoid arthritis and ankylosing spondylitis).1 Compression of the occipital nerve has been described along its course up the neck-while exiting from the semispinalis capitis or trapezius muscles-from everyday activities such as leaning against the back of a chair for an extended period of time. There are also rare occurrences where structural pathology like tumors involving the 2nd and 3rd cervical dorsal roots and sometimes developmental abnormalities can also be causative.
Symptoms and Signs
The pain associated with greater occipital neuralgia is intermittent, sharp, jabbing or throbbing and usually starts in the suboccipital region at the base of the skull near the midline, involves the entire posterior and lateral scalp, and usually radiates towards the vertex. Insult or injury to the lesser occipital nerve will cause pain around the mastoid process and radiate to areas near the ear and lower temple. Pressure on the suboccipital region over the occipital nerve will reproduce pain with radiation. Severe cases may actually have Tinel’s sign in which tapping on the area of the nerve causes sharp, throbbing pain and tingling. One may encounter extreme tenderness upon palpation over the occipital notches and upper cervical region with paroxysms of pain. On sensory exam, there may be hypesthesia or dysesthesia or paresthesia in the posterior scalp. Patients may also report spasms of the para vertebral muscles and restriction of neck movements.
Diagnosis is mainly clinical and based on the localization of pain aligned with the distribution of the occipital nerves. An abnormal neuroexam should prompt imaging of the brain with MRI of cervical spine. The usual MRI sequences are not able to visualize the structural anatomy of the occipital nerves unless there is a gross abnormality like a large tumor.
Occipital neuralgia can present like migraine, with unilateral, throbbing pain especially when it radiates to the frontal, orbital and periorbital region.2 Sometimes nausea, vomiting, photophobia or phonophobia, and eye changes may accompany occipital neuralgia and mimic a migraine. The situation is further complicated by the ability of occipital nerve blocks to relieve migraine headaches and the fact that both these disorders seem to coexist. One study showed that out of 500 patients suffering from migraine headache, almost 40% treated by occipital nerve block had relief of their migraine.
One way to distinguish the two is that typical acute treatment for migraine like the Triptans or ergot alkaloids will not work for occipital neuralgia. The explanation for this seemingly common overlap in presentation is based on neuroanatomical pathways. The C2, C3 nerves project to the nucleus caudalis of the trigeminal nerve, which as we now know, is a key player in generation of migraine headaches. Greater occipital neuralgia probably triggers the pain pathways arising from the nucleus caudalis and therefore can conceivably trigger a migraine attack. In a headache patient, examination should therefore include a thorough examination of the back of the head, and base of neck for tenderness along occipital nerves, apophyseal joints and mobility of the cervical spine.
The initial treatment is symptomatic with analgesics, muscle relaxants, soft cervical collar and physical therapy with gentle range of motion exercises especially head flexion. Local nerve blocking injections with steroids and local anesthetics can be very helpful for symptomatic relief of pain.3 It is hypothesized that depomedrol, a commonly used depot steroid agent for local nerve blocks causes demyelination of the nerve fibers and therefore provides relief of symptoms.
Surgical ablation procedures include sectioning either the peripheral nerve in the scalp or at the 2nd and 3rd cervical roots for medically intractable cases. Occipital nerve release has been attempted in one case series under the presumption that the nerve is commonly trapped while exiting either the trapezius or semispinalis muscle.4 Complete pain relief was not attained in any patient. The benefit from the surgery appeared short-lived and complications included denervation pain and neuroma formation along with recurrence or worsening of pain. Peripheral nerve electrostimulation is a relatively new modality of treatment where subcutaneous electrodes are placed on the occipital nerve which are then stimulated by a small distal generator placed superficially in the abdomen.5
This is a rare type of neuropathic pain originating from the 9th (glossopharyngeal) and sometimes also the 10th (Vagus) cranial nerves. It is therefore also called vagoglossopharyngeal neuralgia.6 The glossopharyngeal nerve exits from the skull through the jugular foramen, behind the styloid process, to supply the tongue and pharynx (see Figure2). It is responsible for sensory and motor supply to the pharynx, taste and general sensations from the back of the tongue, external ear and internal surface of the tympanic membrane, and salivation (supply to parotid gland). It also receives fibers from the carotid body and sinus and participates in the maintenance of blood pressure and sympathetic tone of blood vessels.
It is usually idiopathic in nature. Secondary causes include nerve compression while exiting the neck by trauma, local infection or an elongated styloid process or tumors.7 Recent improvement in imaging techniques has resulted in better diagnosis of secondary causes of the neuralgia due to compression of the nerve root at its entry zone by an artery (vertebral or posterior inferior cerebellar artery) or vein and distortion by tumors like papillomas.