Crocodile Tears Syndrome – Causes, Symptoms, Treatmment

Anatomy?

The anatomy of the facial nerve is a mixed nerve that has a motor, sensory, and parasympathetic components.

The facial nerve has the following functional components:

• The special visceral efferent component (branchial motor) that innervates the muscles of facial expression, stylohyoid, posterior belly? of digastric and the stapedius muscle which are derived from the second branchial arch.
• General visceral efferent (visceral motor) gives autonomic (parasympathetic) innervation to the lacrimal, salivary, and mucosal glands.
• Special visceral afferent (special sensory) carries taste sensation from anterior two-thirds of the tongue.
• General somatic afferent (general sensory) carries sensation from the skin of concha of the external ear.

Facial Nerve Nuclei

The facial motor nucleus (sympathetic) is a collection of lower motor neurons in the lower part of pons innervating the muscles of facial expression and stapedius. The part of the nucleus supplying the muscles of the lower half of the face receives cortico-nuclear innervation from the opposite hemisphere whereas the part of the nucleus supplying the muscles of the upper part of the face receives bilateral? corticonuclear innervation.

Behind the motor nucleus are the superior salivatory and lacrimatory nuclei which are parasympathetic. The superior salivatory nucleus receives information from the hypothalamus and taste sensation from the oral cavity. It innervates the submaxillary and sublingual salivary glands via preganglionic fibers.

The lacrimatory nucleus receives information related to emotional responses from the hypothalamus. Information from the sensory nuclei of the trigeminal nerve is also received by the lacrimatory nucleus which brings about reflex lacrimation upon irritation of the cornea? or conjunctiva?.

Facial Nerve Course and its Branches

The facial nerve consists of a motor and sensory root. The motor root loops around the abducens nucleus in the floor of the fourth ventricle? and emerges at the junction of pons and medulla along with the sensory root. The 2 roots travel along with the eighth cranial nerve to reach the internal acoustic meatus, and the 2 roots fuse at the lower part of the meatus to form a single trunk. Within the meatus, the nerve gets divided into three parts by 2 bends following which it exits the skull? via the stylomastoid foramen. The facial nerve then crosses the stylomastoid process and enters the parotid gland at its posteromedial surface. It divides into its terminal branches ant the angle of the mandible?:

• Temporal branches
• Zygomatic branches
• Buccal branches
• Mandibular branch
• Cervical? branch

Branches Within the Facial Canal

• Greater (superficial) petrosal nerve arises from the geniculate ganglion?. It carries parasympathetic preganglionic fibers and continues as the nerve of the pterygoid canal to finally synapse with the pterygopalatine ganglion. Postganglionic fibers from the pterygopalatine ganglion synapse with mucosal glands of the nose, palate, pharynx? and also the lacrimal gland.
• The nerve to stapedius supplies the stapedius muscle which dampens excess vibrations of the stapes muscle.
• Chorda tympani carries taste from the anterior two-thirds of the tongue to the brain via the middle ear.

Anatomically, the facial nerve (nervus intermedius) contains fibers for both the submandibular salivary gland and the lacrimal gland. After the facial nerve passes through the geniculate ganglion, the secretomotor fibers for the submandibular salivary gland travel with the main nerve trunk, whereas, the secretory fibers to the lacrimal gland disaffiliate from the facial nerve to join the greater petrosal nerve. These secretory fibers then relay in the sphenopalatine ganglion before innervating the lacrimal gland.

Pathophysiology

In the recovery period following facial nerve injury, the regenerating salivary nerve fibers undergo synkinesis or are misdirected to ultimately innervate the lacrimal gland instead of the submandibular gland. As shown in the figure below, the regenerating nerves are directed toward the lacrimal gland via the greater superficial petrosal nerve (GSPN). The result is that any stimuli such as the smell or taste of food, instead of causing salivation, excites the lacrimal gland to produce ipsilateral tearing.[rx]

Another theory put forth by Spiers et al. is a congenital? abnormality?. This was supported by the finding that few patients with crocodile tears syndrome also had underlying lateral rectus palsy or co-existing with Duane retraction syndrome. It was suspected for the lesion? to be in the pons adjacent to the abducens nerve.[rx] Another mechanism for crocodile tears syndrome is thought to be the formation of an artificial synapse at the injury site. This synapse allows the impulses to jump from one fiber to another and crossovers are likely, leading to crocodile tears syndrome.[rx]

Causes of Crocodile Tears Syndrome

There are different theories regarding the cause of crocodile tears syndrome. The widely accepted theory is due to Bell’s palsy or traumatic disruption of the nervus intermedius.

Diagnosis? of Crocodile Tears Syndrome

History and Physical

Crocodile tears syndrome involves unilateral? lacrimation or tearing whenever the patient is eating or drinking. However, bilateral cases have also been recorded by Speirs et al.[6] On clinical? and slit-lamp examination of the eye and the lacrimal appendages, it appears within normal limits. This rules out other causes of epiphora such as lacrimal duct obstruction, chronic? dacryocystitis, punctal stenosis?, conjunctivitis, and foreign body in the conjunctiva. Crocodile tears syndrome is mostly a diagnosis of exclusion in patients with a prior history of facial nerve palsy. Patients with the previous incidence of Bell’s palsy may give a history of acute?-onset? symptoms of neck, mastoid or ear pain?, altered taste or facial sensation, and hyperacusis.

Evaluation

Crocodile tears syndrome is a diagnosis of exclusion. Slit lamp examination of the eye and appendages is usually done to rule out other causes of epiphora. The basal tear secretion of an individual can be assessed by using the Schirmer’s test. In the case of crocodile tears syndrome, it can be performed before and after gustatory stimulation to document increased tearing after salivation. It is also important to rule out other differentials.

• Orbicularis oculi weakness? due to facial palsy – The orbicularis oculi muscle is tested by asking the patient to shut his or her eyes tightly while the examiner tries to open them. The force required to open the eyelid can be graded, and accordingly, the degree of muscle weakness? can be ascertained.
• Paralytic ectropion – The examiner performs the snap-back test to check for the lower lid laxity. A positive test is obtained when the eyelids spring back immediately into their original position after being pulled down by the examiner.
• Nasolacrimal duct obstruction – ROPLAS (regurgitation on pressure over lacrimal sac) test is used to ascertain nasolacrimal duct obstruction.

Treatment of Crocodile Tears Syndrome

Historically, many different treatment options have been used to stop the lacrimation. A 5% solution of guanethidine was used to block the adrenergic receptors in the lacrimal gland.[rx] Peroral treatment with propantheline bromide 30 mg was also tried.[rx] It was also believed that instilling 1% homatropine hydrobromide in the conjunctival sac would lead to a secretomotor nerve blockade.[rx]However, the side-effects of these pharmacological modulations outweighed their therapeutic? outcome and thus, presently, they are not the preferred line of treatment.

Surgical options include excision of the palpebral lobe of the lacrimal gland, cutting of the chord tympani nerve, denervation of the lacrimal gland either by dissection or diathermy, and sphenopalatine ganglion blockage by alcohol or cocaine, and vidian neurectomy.[rx] Nevertheless, these options are redundant, drastic, and have persistent side-effects such as vision loss and total ablation of the lacrimal gland.

The treatment of crocodile tears syndrome depends on the severity of the hyperlacrimation and the need of the patient. Mild? cases are generally managed by counseling and regular monitoring. Less drastic surgical options are used, and they are proving to be an effective way to control the tearing. Subtotal resection of the palpebral lobe of the lacrimal gland is considered beneficial by McCoy et al., and pre-operative Schirmer’s test helps to control the amount of gland to be resected and thus preventing dry eye.[rx]

The most widely accepted treatment of crocodile tears syndrome is botulinum toxin injection into the lacrimal gland.[rx] Botulinum toxin-A is an acetylcholine release inhibitor and acts at the neuromuscular junction. It acts by stopping transmission along the aberrantly regenerated parasympathetic nerve fibers to the affected gland. It can be administered both transcutaneously and transconjunctivally to the lacrimal gland in crocodile tears syndrome patients.[rx] The botulinum toxin dose injected into the lacrimal gland is 2.5 units and its effect lasts for around 6 months.[rx] Transconjunctival route of injection into the palpebral route is proven to have lesser complications than injecting transcutaneously. Montoya et al report that the injection of botulinum toxin into the lacrimal gland in crocodile tears syndrome is a safe and effective method for treating excessive tearing.[rx]