Bell's palsy pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Pathophysiology
Microscopic Pathology
- The facial nerve has an edematous, thickened perineurium with infiltrates of inflammatory cells between nerve bundles and around blood vessels.
- It appears that the histology of the facial nerve in Bell's palsy is similar to Herpes Zoster infection, suggestive of an infectious cause.
Associated Conditions
Bell’s Palsy-induced Blepharospasm
Blepharospasm associated with Bell's palsy has been rarely reported. Instead of the classic presentation with the affected eye wide open, the affected eye is closed shut, with the patient unable to open it(Blepharospasm).
- So far, seven patients previously reported: all women.
- In five of the seven patients, blepharospasm appeared within a month after the onset of Bell’s palsy.
Possible Mechanisms
- The majority of patients with blepharospasm have a high incidence of local ocular symptoms prior to or at the onset of blepharospasm, such as blepharitis, conjunctivitis, dry eyes or photophobia.
- Chronically disturbed sensory inputs to the central nervous system due to lagophthalmos and corneal irritation may contribute to the generation of blepharospasm.
- In patients with Bell’s palsy, there is an enhanced blink reflex secondary to inputs from the paralyzed side compared which those of the non-paralyzed side.
- Abnormal afferent input from the paralyzed side contributes to the abnormal sensitization of the blink reflex, thus facilitating the induction of abnormal facial motor outputs such as blepharospasm.
- It is unclear why Bell’s palsy-induced blepharospasm is extremely rare.