Although Bell’s palsy has been described as idiopathic facial paralysis, many evidence suggest a viral etiology. McCormick postulated the etiologic agent to be the herpes simplex virus in 1972. Studies by Murakami strongly suggest that herpes simplex virus type 1 (HSV-1) is active in cases of Bell’s palsy. In this study, endoneural fluid from 11 of 14 patients undergoing transmastoid decompression during the acute phase of the disease displayed DNA fragments of HSV-1 via the polymerase chain reaction (PCR). None from this surgical group displayed evidence of herpes zoster or Epstein Barr virus in the obtained samples. Again, finding of HSV-1 DNA in a temporal bone section of a patient dying six days after developing Bell’s palsy. An animal model for Bell’s palsy has been developed in which animals inoculated with HSV-1 demonstrate transient facial paresis, thus further supporting the idea that Bell’s palsy is the result of a viral inflammatory response that induces edema within the facial nerve.
The meatal segment of the facial nerve and the nervus intermedius remain in the anterior-superior quadrant of the IAC and enter the fallopian canal at the meatal foramen, superior to the transverse crest and anterior to the vertical crest (Bill’s bar). Ge and Spector (14) have determined that the narrowest portion of the fallopian canal is located at the meatal foramen (mean diameter .68 mm). Thus, the size of the foramen coupled with a tight arachnoid band located at this segment contributes to the constriction of the facial nerve at this point in Bell’s palsy. The labyrinthine segment of the nerve, encased within the narrowest portion of the fallopian canal, courses 2-4 mm to the geniculate ganglion, where the nerve takes an acute turn at the external genu to enter the middle ear. The tympanic segment (horizontal segment) courses a total of 11 mm slightly above the cochleariform process and oval window and turns into the second turn (pyramidal turn) inferior to the lateral semicircular canal. The mastoid segment (vertical portion) then descends 13 mm to the stylomastoid foramen (2).
Sunderland's classification describes five degrees of nerve injury. The first degree (neuropraxia) involves a localized conduction block in the nerve with the nerve fibers responding to electrical stimuli proximal and distal to the lesion, but not across the injured segment. Axonal continuity is preserved, wallerian degeneration does not occur, and recovery is usually complete. The second degree of nerve injury is called axonotmesis. This refers to disruption of the axon into proximal and distal portions with interrupted axoplasmic flow and Wallerian degeneration. The third, fourth, and fifth degree of nerve injury are grouped together as neurotmesis, and subdivided depending on the integrity of perineurium and epineurium. Wallerian degeneration occurs at the faster rate than axonotmesis and prognosis is the poorest. The rate of nerve degeneration in Bell’s palsy falls in between axonotmesis and neurotmesis. However, there is no electrical test to-date that can quantitatively differentiate the two subclasses of injury.
The efficacies of oral prednisone and anti-viral agents have been studied extensively, yet there is no consensus among experts on ideal regimen and dosage.Adour, whose double-blind randomized controlled trial shows that the combined therapy of prednisone and acyclovir results in better return of muscle function and prevention of partial nerve degeneration.
This result is challenged by another prospective trial by Kawaguchi who illustrates that valacyclovir plus prednisone have no advantage over prednisone alone.
Herpes virus detection in Bell’s palsy R. Filipo G. Balsamo E. Covelli G. Attanasio O. Turriziani G. Antonelli
VIRAL ETIOLOGY <ul><li>McCormick (1972) – herpes simplex virus </li></ul><ul><li>Murakami (1996) </li></ul><ul><ul><li>11/14 patients with HSV-1 in endoneural fluid </li></ul></ul><ul><ul><li>None in controls or Ramsay-Hunt syndrome </li></ul></ul><ul><li>Temporal bone section at autopsy </li></ul><ul><li>Animal model inoculated with HSV-1 </li></ul>
<ul><li>intra canal facial nerve haedema, with compression at the meatal foramen </li></ul><ul><li>stylomastoid foramen </li></ul>Activation and/or re-activation of Herpes Simplex type I in the geniculate ganglion due to internal or external triggers inflammatory reaction VIRAL ETIOPATHOLOGY
ANATOMY Gh. Lacrimale Ner. Lacrimale Gh. Sottomandibolare Gh. Sottolinguale N. linguale N. stiloioideo Corda timpani Stylomastoid foramen Parotide Forame ovale N. Grande petroso CUI Ganglio otico Geniculate ganglion Iatus petroso Mm. facciali Digastrico Stapedius Nervo vago Fibre secretorie (lacrimali e salivari) Fibre gustative dei 2/3 ant. della lingua N. vidiano Plesso carotideo I II III 74° 95-120° meatal foramen (mean diameter .68 mm)
SUNDERLAND CLASSIFICATION OF PERIPHERAL NERVE INJURY Neurapraxia Axonotmesis Neurotmesis <ul><ul><li>no axonal discontinuity </li></ul></ul><ul><ul><ul><li>Wallerian degeneration (distal to lesion) </li></ul></ul></ul><ul><ul><ul><li>Axoplasmic disruption, endoneural sheaths intact </li></ul></ul></ul><ul><ul><ul><li>Wallerian degeneration (distal to lesion) </li></ul></ul></ul><ul><ul><ul><li>Axon disrupted, loss of tubules, support cells destroyed </li></ul></ul></ul>PATHOPHYSIOLOGY HSV reactivation leads to damage of facial nerve
<ul><li>Double-blind RCT </li></ul><ul><li>99 Bell’s palsy patients </li></ul><ul><li>Combined therapy (acyclovir and prednisone) is better than placebo and prednisone, in terms of: </li></ul><ul><ul><li>Return of muscle motion </li></ul></ul><ul><ul><li>Prevention of partial nerve degeneration </li></ul></ul>STEROID VS. STEROID + ACYCLOVIR Adour KK 1996 Ann Otol Rhinol Laryngol. 1996 May;105(5):371-8
<ul><li>Prospective RCT of 150 patients </li></ul><ul><li>No significant difference in recovery </li></ul>STEROID VS. STEROID + ACYCLOVIR Kawaguchi: Laryngoscope, Volume 117(1).January 2007.147-156 Prednisolone Prednisolone + Valacyclovir
MATERIAL AND METHODS 53 PATIENTS 94,4 % (50 pts) 3 pts
63% right 27% left MATERIAL AND METHODS 53 PATIENTS
CHARACTERISTICS OF THE STUDY FROM A VIROLOGICAL POINT OF VIEW <ul><li>Early administration of therapy </li></ul><ul><li>Early time of specimen collection </li></ul><ul><li>Virological analysis </li></ul><ul><ul><li>serology; </li></ul></ul><ul><ul><li>virus isolation in saliva </li></ul></ul><ul><li>Virological analysis in progress </li></ul><ul><ul><li>real-time PCR instead of standard PCR in saliva </li></ul></ul><ul><ul><li>cytokine profile including interferon in blood and PBMC </li></ul></ul>VERO MRC-5 cells Within 48 hrs from the onset of the paralysis
RESULTS Prevalence of Anti-HSV-1 antibody Prevalence of Anti-VZV antibody IgM+ Grey zone IgM+ IgG+ IgG+ IgM+ Grey zone IgM+ 8 pts 5 pts 50 pts 48 pts
RESULTS Prevalence of Anti-HSV-1 antibody Prevalence of Anti-VZV antibody IgM+ HSV-VZV 8% (4pts) 4 pts 1 pt
RESULTS <ul><li>In a low percentage of the 53 patients included in the study a re-activation of HSV-1 or VZV seems to occur (15% and 10%). </li></ul><ul><li>A cross-reactivity (8%) has been observed between HSV and VZV IgM+ groups </li></ul><ul><li>DNA viral isolation in saliva was invariably negative. </li></ul>
PRELIMINARY RESULTS <ul><li>Presence of HSV-1 DNA: about 20% </li></ul><ul><li>Presence of VZV DNA: about 10% </li></ul><ul><li>In all of the IgM+ pts the presence of VZV has been documented. </li></ul>real time PCR in saliva
CONCLUSIONS <ul><li>low percentage of IgM seroconversion </li></ul><ul><li>low detection of DNA virus by very sensitive molecular technique (preliminary evidence) </li></ul><ul><li>lack of significant correlation between IgM+ patients and their baseline grade of facial paralysis </li></ul><ul><li>most of the literature data </li></ul>herpesvirus cannot entirely explain the etiopathogenesis of Bell’s palsy