Idiopathic facial paralysis

29 Idiopathic facial paralysis




INITIAL PRESENTATION



Acute


Dropped or drooping flaccid upper and lower lips, dropped ear, lopsided face, odd look to face, food collecting in the mouth between the flaccid lip and the teeth, dropping food, drooling saliva (and secondary head shaking), inability to blink, sleeping with eyes open, widened palpebral fissure, dry eye, corneal ulcers, dry nose and deviation of the nose can all occur (Fig. 29.1).



Chronic


Elevation of the lip and ear, widening of the palpebral fissure and contracture of the facial muscles can occur.


image

Figure 29.1 Acute paralysis of R VII. The right ear is slightly more ventral. The right upper lip is noticeably lower.



INTRODUCTION


The facial nerve innervates the:


• Muscles of facial expression: ears, eyelids, lips, cheeks and nose

• Sublingual and mandibular salivary glands

• Nasal and lacrimal glands.

It also transmits sensory fibres from the taste buds of the rostral tongue but dysfunction is not noticed.


Facial nerve lesions typically cause paralysis of the muscles of facial expression. In time, the flaccid muscles atrophy, undergo fibrosis and contracture and thus assume a more normal position. Voluntary and reflex movement of the contracted muscles is still absent. The contracture does not relax under GA.


LMN paresis or paralysis is the most common sign of dysfunction, however ‘positive’ signs of nerve irritation have been reported:






Hemifacial spasm

is a unilateral regular tonic-clonic contraction of one or more muscles of facial expression. It results from an irritation of the facial nerve but has been reported in dogs in concert with intracranial masses physically distinct from the facial nerve. The spasm relaxes under general anaesthesia which helps distinguish it from the fibrosis and contracture secondary to chronic facial paralysis.


Animals present with facial asymmetry, elevation and wrinkling of the upper lip, caudal displacement of the labial commissure, blepharospasm, elevation of the ear, deviation of the nose to the ipsilateral side and hyperactive palpebral (blink) reflex.


Myotonia causes a delayed relaxation of muscle following stimulation. This could give the appearance of a hemifacial spasm. Focal tetanus is limited to the limbs. The face is affected bilaterally in generalized tetanus. Other differentials of hemifacial spasm include: myokymia, blepharospasm, facial tic and partial seizure.



Epiphora

is an increased tear production and appears as overflowing tears or tear staining of the medial canthus.


Reflex lacrimation occurs in response to eye pain which should be evident on examination. Owners sometimes report epiphora occurring a few days before ipsilateral facial paralysis develops. Parasympathetic stimulation from organophosphate toxicity results in SLUD (salivation, lacrimation, urination, defecation).


Obstruction of the tear duct is a common cause of tear staining.


Paradoxical (‘crocodile’) tears occur in the human during and immediately after eating as a rare phenomenon secondary to aberrant reinnervation of CN VII when the fibres innervating the salivary glands are redirected to the lacrimal gland. This may be tested with 1% tropicamide placed on tongue as a sialogogue. Excess tearing is seen in the ipsilateral eye after approximately 1 minute.


The serous glands of the nasal plane are innervated by the facial nerve. A wet nose with clear watery (serous) nasal discharge from one or both nostrils may be normal and has not been recognized as an early sign of impending facial nerve paralysis. It is an unreliable indicator of general wellbeing – hence the thermometer’s supremacy. Systemic causes are usually bilateral and include: over-hydration, early sign of nasal irritation by fungi, parasites, foreign bodies, neoplasia, viruses, or allergies. Rhinorrhoea is the leakage of CSF by the nose and is reported following head trauma.

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  4. LMN paresis and paralysis: Brachial plexus avulsion

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Sep 3, 2016 | Posted by in SMALL ANIMAL | Comments Off on Idiopathic facial paralysis

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