|Major||Sensory loss in face||Weak muscles of facial expression|
|Minor||Jaw movements impaired||Reduced sense of taste in anterior ⅔ of tongue|
Sensory changes most frequently follow nerve damage from trauma. Weakness of the facial muscles is most commonly seen in neurological disorders and presents with paralysis (palsy) but is also seen in primary muscle disease and neuromuscular junction disorders, is then usually symmetrical, and the uncommon causes include:
Normal facial sensation, mediated by the trigeminal nerve, is important to protect the skin, mucosae and especially the cornea of the eye from damage. Facial sensory changes, which can be caused by lesions of a sensory branch of the trigeminal nerve or the central connections (Fig. 20.1), may lead to sensory awareness that is:
Sensory defects may lead to unrecognized damage from trauma or burns (‘trophic lesions’), and are occasionally associated with hyperaesthesia (i.e. the patient has a decreased sensory perception, but when sensation is perceived, it may cause discomfort).
This is the usual cause of sensory loss – especially after orthognathic or cancer surgery. Ipsilateral hypoaesthesia or anaesthesia usually result. If the nerves are stretched or compressed (neuropraxia), there is often only hypoaesthesia, and recovery of sensation is speedy, typically within days. However, if the nerves are severed (neurotmesis), anaesthesia is profound and recovery is delayed for months accompanied by paraesthesia or hyperaesthesia. Recovery is sometimes not complete: repair may be indicated:
Nasopharyngeal carcinomas may invade the pharyngeal wall to infiltrate the mandibular division of the trigeminal nerve, causing pain and sensory loss in the region of the inferior alveolar, lingual and auriculotemporal nerve distributions; invade the levator palati to cause soft palate immobility; and, by occluding the Eustachian tube, cause deafness (Trotter syndrome).
since other cranial nerves are anatomically close, there may be associated neurological deficits in intracranial causes of facial sensory loss. Thalamic strokes in particular can cause facial sensory loss
syringobulbia: this leads to sensory loss spreading from the periphery of the face inwards towards the nose, plus a lower motor nerve lesion of the vagus, hypoglossal and accessory nerves, leading to disturbances of speech and swallowing, and bilateral upper motor neurone lesions affecting all limbs. A ‘syringomyelia-like’ syndrome has been infrequently reported in neurological disorders such as Tangiers disease, lepromatous leprosy and a novel syndrome termed ‘facial onset sensory and motor neuronopathy syndrome’ (FOSMN).