A patient presents with the complaint of inability to close the eye, drooling of saliva, and deviation of the angle of the mouth. Which of the following nerves is most likely to be affected?

Correct Answer: C. Facial nerve

The clinical triad of inability to close the eye (lagophthalmos), drooling of saliva, and deviation of the angle of the mouth (deviation of commissure) is pathognomonic for facial nerve (CN VII) palsy. The facial nerve has five major motor branches: temporal, zygomatic, buccal, marginal mandibular, and cervical. Inability to close the eye indicates paralysis of the orbicularis oculi (supplied by temporal and zygomatic branches). Drooling and mouth deviation indicate paralysis of the muscles of facial expression, particularly orbicularis oris and buccinator (supplied by buccal and marginal mandibular branches). In India, Bell's palsy (idiopathic CN VII palsy) is the most common cause, though viral infections (HSV-1, VZV in Ramsay Hunt syndrome), otitis media with temporal bone involvement, and parotid pathology must be excluded. The combination of upper and lower facial weakness affecting both eye closure and mouth symmetry is diagnostic of CN VII involvement, as opposed to central lesions which spare the upper face due to bilateral innervation of the forehead muscles.

Why the other options are wrong

A. Glossopharyngeal nerve — The glossopharyngeal nerve (CN IX) innervates the stylopharyngeus muscle and carries taste from the posterior third of the tongue and sensation from the pharynx. It does not innervate muscles of facial expression, orbicularis oculi, or muscles controlling mouth commissure. Glossopharyngeal palsy presents with dysphagia and loss of gag reflex, not facial droop or eye closure inability. B. Trigeminal nerve — The trigeminal nerve (CN V) is sensory to the face and motor to muscles of mastication (masseter, temporalis, medial/lateral pterygoids). Trigeminal nerve lesions cause jaw deviation toward the affected side and loss of corneal reflex, but do NOT cause inability to close the eye, drooling, or mouth commissure deviation. The motor functions are entirely different from facial expression. D. Oculomotor nerve — The oculomotor nerve (CN III) innervates extraocular muscles (medial rectus, superior rectus, inferior rectus, inferior oblique) and levator palpebrae superioris. Oculomotor palsy causes ptosis, ophthalmoplegia, and pupillary dilation, but does NOT affect orbicularis oculi function, facial expression, or mouth commissure. It does not cause drooling or facial asymmetry.

High-Yield Facts

Mnemonics

CN VII Motor Functions: FACEBROW Forehead (temporal) – Frontalis | Around eye (zygomatic) – Orbicularis oculi | Cheek (buccal) – Buccinator | Eye closure (zygomatic) – Orbicularis oculi | Buccal (buccal) – Mouth muscles | Rising mouth (marginal mandibular) – Depressors of lower lip | Oral (cervical) – Platysma | Whole face – CN VII. Use when identifying which nerve controls facial expression. Facial Palsy Red Flags: RAMSAY Recurrent palsy | Aural vesicles (Ramsay Hunt) | Multiple nerve involvement | Severe pain | Abnormal imaging | Young age with bilateral palsy. If present, rule out secondary causes (not idiopathic Bell's palsy).

NBE Trap

NBE may pair trigeminal nerve (CN V) with facial droop to trap students who confuse the motor functions of CN V (mastication) with CN VII (facial expression). The key discriminator is that CN V does NOT control orbicularis oculi or mouth commissure muscles — only CN VII does.

Clinical Pearl

In Indian clinical practice, a patient presenting with acute unilateral facial paralysis and inability to close the eye should be evaluated urgently for Bell's palsy (most common) or Ramsay Hunt syndrome (if vesicles or otalgia present). Early high-dose corticosteroids (prednisolone 1 mg/kg/day × 7 days) and eye care (lubricating drops, protective taping, eye mask at night) are critical to prevent corneal scarring and permanent disability — a common complication in delayed presentations.

_Reference: Harrison Ch. 379 (Cranial Nerve Disorders); Robbins Ch. 28 (Peripheral Nerve Pathology); Bailey & Love Ch. 38 (Facial Nerve Disorders)_