Bell’s palsy and other cranial nerve lesions, including trigeminal neuralgia
Description
CN VII - the anatomy generates the localising signs
Branches leave in order; the most proximal deficit sets the level.
| Branch (proximal -> distal) | Function | Lost if lesion is at/above |
|---|---|---|
| Greater petrosal | Lacrimation | Geniculate ganglion |
| Nerve to stapedius | Damps loud sound | Middle ear -> hyperacusis |
| Chorda tympani | Taste anterior 2/3 tongue, submandibular/sublingual secretion | Distal to stapedius -> dysgeusia |
| Motor to face | All muscles of facial expression, platysma, stylohyoid, post. digastric | Any level |
- Bell's palsy - acute idiopathic LMN facial palsy
- Peaks by ~72 h; unilateral; +/- retroauricular/mastoid pain, dysgeusia, hyperacusis, subjective facial numbness (objective V loss is not Bell's)
- Ramsay Hunt (herpes zoster oticus) - VZV reactivation in the geniculate ganglion
- Facial palsy + vesicles in the ear canal/concha/palate + severe otalgia + numb anterior tongue
- Often VIII too -> vertigo, SNHL. Worse prognosis than Bell's; vesicles may appear after the palsy
- Trigeminal neuralgia - paroxysmal, unilateral, electric shock-like pain in a V distribution
- Seconds to 2 minutes, triggered by light touch (chewing, cold wind, shaving, brushing teeth)
- V2 and/or V3 in ~95%; V1 alone rare; refractory period after an attack
- Classic = neurovascular compression (superior cerebellar artery) | Secondary = MS plaque, tumour | Idiopathic
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