Your next patient noticed the left side of his face drooping since this morning and cannot fully close his eye. Here's how the Bell's palsy case unfolds and what to pick up on the way.

A bell's palsy case can be easy to mislabel as a stroke if you rush the history. Your next patient noticed the left side of his face drooping since this morning and cannot fully close his eye. He says, "He woke this morning with one side of his face drooping." The trap is missing forehead involvement and the sudden waking onset, then overlooking sensory clues like altered taste or hyperacusis. The page walks through how this case presents, what to pick up in the history, the bedside findings that point to a lower motor neurone facial palsy affecting the whole side, how to separate it from a central pattern that spares the forehead and usually has other neurology, the tests to consider, and the teaching points, including careful exclusion of ear vesicles and other cranial or limb findings, and when to think about Lyme disease or diabetes.

How the case presents

Your next patient noticed the left side of his face drooping since this morning and cannot fully close his eye. In their own words: "He woke this morning with one side of his face drooping."

Observations on arrival:

Observation	On arrival
Heart rate	74 beats per minute
Blood pressure	128/78 mmHg
Respiratory rate	14 breaths per minute
Oxygen saturation	99%
Temperature	36.8 °C

What to pick up in the history

These are the findings the case is built around. Each one moves you towards or away from Bell's palsy, and the scorecard checks whether you found it.

Sudden left facial droop noticed on waking: abrupt unilateral facial weakness on waking is the classic presentation of an acute facial nerve palsy.
Whole side weak including forehead; cannot raise eyebrow: forehead involvement confirms a lower motor neuron lesion and effectively excludes a cortical stroke.
Cannot fully close the left eye, which feels dry: incomplete eye closure risks exposure keratopathy and drives urgent lubrication and taping.
No limb weakness, slurred speech or other neurology: absence of other deficits argues strongly against stroke and against a broader brainstem or cranial nerve lesion.
Altered taste at the front of the tongue and hyperacusis: chorda tympani and stapedial involvement localise the lesion to the facial nerve within the temporal bone.
No rash or blisters in or around the ear.
Viral cold about a week ago: A preceding viral illness fits the presumed reactivation aetiology of Bell's palsy.
Weakness came on over hours, not gradually over weeks: rapid onset fits Bell's palsy; gradual progression would suggest a tumour or parotid mass instead.

Red flags you must not miss

The case marks these as must-elicit. They only come out if you ask.

Sudden left facial droop noticed on waking.
Whole side weak including forehead; cannot raise eyebrow.
Cannot fully close the left eye, which feels dry.
No limb weakness, slurred speech or other neurology.
No rash or blisters in or around the ear.

Investigations and what they showed

MRI internal auditory meatus: May show enhancement of the facial nerve (CN VII) in the internal auditory canal; reserved for atypical cases, other cranial-nerve signs, a mass, or failure to recover. Why it helps: G. acoustic neuroma) when the presentation is atypical or recovery does not occur.
Inspect the face: A one-sided facial droop that involves the whole half of the face. On the affected side the forehead stays smooth when he is asked to raise his eyebrows (the examiner is holding the hairline to show it), the eyebrow sits lower, the nasolabial fold is flattened out and the corner of the mouth is pulled across to the good side when he shows his teeth. Why it helps: forehead involvement is the whole case. Because each frontalis muscle has bilateral cortical input, a stroke spares the forehead; only a lower motor neurone lesion of CN VII weakens it.
Inspect the eyes: On attempted eye closure the eye on the affected side stays open, showing a wide palpebral aperture, an exposed and slightly injected globe and a drooping lower lid; the other eye closes normally. Why it helps: lagophthalmos is the dangerous part of Bell's palsy. An eye that will not close dries out and is at real risk of exposure keratopathy and corneal ulceration, so it needs lubricating drops by day, ointment and taping at night, and urgent review if it becomes red or painful.
Inspect the mouth and oral cavity: The corner of the mouth droops on the affected side and saliva and drink escape from it; food pockets between the cheek and gum on that side because the buccinator is weak. Why it helps: explains his dribbling and difficulty eating, and is the practical reason to warn him about food pocketing and mouth care. It is lower-face weakness, on its own it does not separate Bell's palsy from a stroke, which is why the forehead must always be tested.
Inspect the eyelids: On forced eye closure the lids on the affected side do not meet and the eyeball is seen rolling upwards and outwards behind the gap, Bell's phenomenon. The lower lid also sags away from the globe and the eye waters. Why it helps: bell's phenomenon is a normal protective reflex made visible by the palsy, and its presence confirms a peripheral CN VII lesion. It also tells you the cornea is only partly protected, reinforcing the need for lubrication and night-time taping.

Imaging findings

Otoscopy: Normal ear canal and tympanic membrane, no vesicles/rash (which would suggest Ramsay Hunt/herpes zoster oticus) and no otitis.
CT head: Normal, no infarct or haemorrhage.
CT temporal bones: Normal, the bony facial nerve canal is intact and well corticated along its whole course, with no fracture, erosion or dehiscence; the mastoid air cells and middle ear are fully pneumatised and clear, with no opacification, no mastoiditis and no cholesteatoma.

Why the diagnosis is Bell's palsy

The decisive diagnosis is bell's palsy, an idiopathic, acute lower-motor-neuron (LMN) palsy of the facial nerve (CN VII). The single most important discrimination is LMN versus UMN: in an LMN facial palsy the whole side of the face is weak including the forehead (cannot wrinkle the forehead/raise the eyebrow, cannot close the eye), pointing to Bell's; in an UMN/central lesion (stroke) the forehead is spared (bilateral cortical innervation) and there are usually other neurological signs. Bell's is a clinical diagnosis of exclusion: examine the ear (herpetic vesicles = Ramsay Hunt), check for other cranial nerves/limb signs (stroke, tumour, MS, Guillain, Barré), and consider Lyme disease/diabetes. g. Most patients recover well over weeks to months. 'Peripheral neuropathy' is the broad category (an LMN cranial mononeuropathy), but the specific idiopathic diagnosis here is Bell's palsy, and the essential safety step is confidently distinguishing it from a stroke.

Bell's palsy at a glance

What it is

Bell's palsy is a sudden, idiopathic weakness of the facial nerve (cranial nerve VII) affecting one side of the face, including the forehead. It is the most common cause of facial paralysis worldwide and is a diagnosis of exclusion, made once other causes of facial weakness have been considered and ruled out.

Pathogenesis

The leading theory is that a viral infection, most often herpes simplex virus, causes inflammation and swelling of the facial nerve as it passes through the narrow bony facial canal in the temporal bone. This swelling compresses the nerve within its own canal, blocking conduction to every muscle it supplies on that side, which is why the whole side of the face, including the forehead, is affected rather than sparing it.

Who it affects

Fairly common: about 1 in 60 to 70 people are affected during their lifetime, with 15 to 40 cases per 100,000 people each year, affecting both sexes roughly equally. Diabetes, pregnancy (especially the third trimester), and a recent upper respiratory infection all raise risk.

How serious it is

The great majority of patients recover well: about 70% recover completely, most within three weeks, with further improvement over months. A small proportion are left with residual weakness or synkinesis (involuntary associated movements). The main immediate danger is exposure keratopathy from an eye that cannot close properly, which is preventable with simple eye care.

Causes and risk factors

The exact trigger is unknown, but reactivation of herpes simplex virus within the facial nerve is the leading theory. Diabetes, pregnancy, and recent viral upper respiratory infection are recognised risk factors. There is no way to prevent it, and it is not inherited.

Investigations and lab tests

Bell's palsy is a clinical diagnosis: examine the ear for vesicles (Ramsay Hunt syndrome), check the other cranial nerves and limbs for additional deficits, and consider Lyme disease or diabetes as contributing causes. Typical Bell's palsy does not need urgent imaging. MRI is reserved for atypical features: other cranial nerve signs, a suspected mass, gradual onset, bilateral palsy, or failure to recover as expected.

At a glance: Diagnose: clinical exam, check forehead involvement and the ear canal. Exclude mimics: other cranial nerves, limbs, Lyme, diabetes. Reserve MRI for atypical cases only.

Teaching points

Bell's palsy is an idiopathic acute lower-motor-neuron palsy of the facial nerve (CN VII).
The KEY discrimination is LMN vs UMN: an LMN facial palsy weakens the whole side including the forehead (can't wrinkle the forehead/close the eye); a central (stroke) palsy spares the forehead and usually has other neurology.
It is a clinical diagnosis of exclusion, examine the ear (Ramsay Hunt vesicles), check other cranial nerves/limbs, and consider Lyme disease and diabetes.
Protect the EYE: lubricating drops by day, ointment and taping the eye shut at night (± patch), because the eye cannot close and is at risk of exposure keratopathy.
G.
Typical Bell's palsy does not need urgent imaging; reserve MRI for atypical features, other cranial-nerve signs, a mass, or failure to recover.
Most patients recover well over weeks to months; incomplete palsies have the best prognosis.
Reconsider the diagnosis (tumour, MS, Guillain, Barré, Lyme, parotid mass) if there are additional signs, gradual onset, bilateral palsy, or no recovery.
Safety-net: review for a red/painful eye, deterioration, or lack of recovery.

Practise a similar case

Reading a case is one thing, but finding the thread yourself under a bit of pressure is different. You have to decide fast if the forehead is weak, while keeping other neurology in mind. Try another simulated neurology history and see what you pick up.

Here's one from the same specialty, with the diagnosis left for you to find. Your next patient has been increasingly confused, very sleepy and unsteady for 6 weeks, though he says he’s all right. Take this patient's history in Diagnosica. It's free to start, no card needed.

Bell's palsy case presentation: history, findings and tests