Biting, scratching, chewing and auto-amputation of digits
are rare but can occur with sensory neuropathies (Fig. 72.1). Cauda equina compression in dogs may result in self-mutilation of the perineum, tail or pelvic limbs.
Figure 72.1 A 4-month-old female Border collie presented for investigation of an arched back and knuckled over hind paws. She had intact patellar reflexes but absent withdrawal reflexes in the hindlimbs. Pain perception was absent in the hind paws and reduced in the forelimbs. The dog later chewed off one of its toes and was euthanized.
Scratching or rubbing the face
is a sign of irritation or pain. The trigeminal nerve is sensory to the face. The facial nerve conveys sensation from the concave surface of the pinna, vertical ear canal and middle ear.
Hypocalcaemia commonly presents with frantic face rubbing.
Trigeminal neuromas are thought to create a paraesthesia of the ipsilateral side of the head which leads to scratching at the face. This generally follows development of ipsilateral atrophy of the masticatory muscles so the diagnosis is self-evident.
Face rubbing is occasionally noted in dogs with facial paralysis. It is not the reason for referral. It may be related to pseudo-ptyalism.
Self-induced excoriations of the head and neck are seen in a small number of cats treated with methimazole or carbimazole within the first 3 months of treatment. Drug withdrawal and glucocorticoids are required.
Episodic pawing at one or both sides of the mouth, with exaggerated licking and chewing movements has been reported in cats, predominantly Burmese. Facial and tongue mutilation may occur. Predisposing factors seem to be dental (periodontal disease, erupting teeth or routine dental treatment) or living in a multi-cat household. No neurological deficits are found. The cause is not known.
The cat had refused to eat or drink for a month, brusquely veering away from the food. At this time, the cat began wiping the left side of its face with a forepaw. Various investigations had been performed to find a source of oral, dental or TMJ pain to no avail. The cat then began having short episodes of sitting still and staring into space. The cat slept deeply and needed shaking to arouse it. The jaw was seen to hang open and the tongue stuck out and made multiple licking movements.
The cat was alert, friendly, ambulatory and had a normal gait, postural reactions and spinal reflexes. The left menace response was present. The left pupil was enlarged and lacked direct and indirect PLR. The left palpebral reflex was absent. Eye movement was normal. The jaw hung partially open and had decreased tone. The lower jaw had intact pain perception. Atrophy of the left masseter muscle could be palpated. The tongue had movement but protruded more than normal. A raspy noise from the upper respiratory tract was heard (Fig. 72.2).
Left CN III because of the mydriasis and lack of pupil constriction. Left CN V because of the lack of sensation to the face, atrophy of masticatory muscles and poor jaw tone. The mandibular branch of CN V was affected because it carries the motor fibres to muscles of mastication. It is also sensory to the lower jaw, but this function remained intact. The raspy URT noise could have been due to laryngeal paralysis.
CN III and CN V lie close together within the cavernous sinus. An invasive skull lesion in the region of the oval foramen and therefore the TMJ was suspected as the cat first presented with a reluctance to eat and rubbing the face, suggesting pain and a possible paraesthesia. No history of ear disease was present so osteomyelitis of the bulla and an otogenic brainstem abscess were not thought to be a realistic differential. CN X departs the skull via the tympano-occipital fissure.