Jay Tor

Hi:

One of my family members has had labyrinthitis a few times. The best strategy we've come with is annual flu shots and avoiding people with strep, etc. The best article I've found to date on this topic is from the emedicine site. Here's a cut & paste on causes, imaging [dx] and treatment. The reason for these specific sections is that in our experience, an accurate diagnosis has been a hit & miss proposition, and too often the antibiotic initially prescribed did not do the job with the result that the pain and damage just continued.

Hope this helps someone.

Good luck,
Jay

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Causes:

The most common cause of LO is bacterial infection of the inner ear that results in suppurative labyrinthitis. Bacterial invasion of the labyrinth can occur via 3 routes: hematogenic spread through the cochlear vasculature, a sequela to otitis media that passes through the round window membrane, or meningogenic spread from the subarachnoid space in meningitis (see Picture 6).

Based on data from 1995, the 3 most common organisms responsible for bacterial meningitis in the United States are H influenzae (0.2 cases per 100,000 population), S pneumoniae (1.1 cases per 100,000 population), and Neisseria meningitidis (0.6 cases per 100,000 population). With the success of conjugate vaccines in preventing invasive H influenzae type b (Hib) disease, S pneumoniae has become the leading cause of bacterial meningitis in the United States. Children younger than 1 year have the highest incidence of pneumococcal meningitis (approximately 10 cases per 100,000 population).

S pneumoniae has the highest incidence of associated LO. The immunogenicity of the S pneumoniae cell wall has been implicated in the propensity to develop LO. In the acute stage, components of the bacterial cell wall trigger local host defenses, which produce a vigorous inflammatory response. In addition, S pneumoniae–induced meningitis generally is treated with bacteriocidal antibiotics that induce hydrolysis of the cell wall and resultant amplification of the inflammatory response. These subcomponents of cell wall teichoic acids are potent activators of the alternative complement pathway. The cells and mechanisms responsible for ossification in LO are unknown; however, several hypotheses have been proposed.

In 1967, Paparella and Sugiura hypothesized that bone-lining cells of the cochlea are pluripotent mesenchymal stem cells that remain uncommitted until stimulated to differentiate into osteoblasts.

In 1985, Kotzias and Linthicum hypothesized that this type of bone originates from osteoblasts within the otic capsule. They suggested that ectopic bone forms on the endosteal layer after inflammatory insult, but the bone is not incorporated beyond the surface.

Additionally, pericytes associated with blood vessels that supply the modiolus and spiral ligament fibroblasts have been hypothesized as cells of origin.

In an antemortem analysis of LO in a human case report, metaplastic bone was reported to have formed within serofibrinous exudate; however, the cell of origin for the osteoneogenesis has not been identified. Because the new bone deposition occurs in continuity with endosteal bone, postmortem studies are not able to differentiate metaplastic bone from osteoplastic bone within the cochlea. The cells and mechanisms responsible for ossification in LO remain undefined.

WORKUP Section 4 of 8

Imaging Studies:

Until recently, LO was diagnosed histologically; however, radiography currently is a tool that can be used to help diagnose LO. Radiographic documentation of osteoneogenesis within the cochlea is possible with a high-resolution computed tomography (HRCT) scan of the temporal bone (see Picture 4 and Picture 5).

In 1 study, some degree of abnormality of the inner ear was noted in 71% of 31 CT scans performed in cochlear implant candidates. Five scans were interpreted as showing ossification within the cochlea. Of these scans, 4 were confirmed at surgery with 1 false-positive result and 1 false-negative result among the 26 scans interpreted as not ossified (4%).

Other authors note a high incidence (63-73%) of CT scan evidence of postmeningitic patients with deafness. They point out that ossification may not always be evident radiographically, with false-negative rates as high as 46%. The high rate of false-negative results may be related to the inability of HRCT scans to detect early histological features of fibrosis and osteoid deposition, which are consistent with the early stages of LO prior to calcification. Despite the exquisite bone detail, HRCT scans may not detect early ossification and soft tissue abnormalities in up to 57% of patients.

Arriaga and Carrier conducted a study that suggests high-resolution, fast spin-echo, T2-weighted MRI is clinically helpful in cochlear implant candidates. This type of MRI study can identify cochlear soft tissue abnormalities in areas of residual cochlear patency in cases of LO. These are soft tissue abnormalities that may not be detected on HRCT scan. This prospective study of 13 consecutive patients receiving preoperative, high-resolution, fast spin-echo, T2-weighted MRI scans of the temporal bone identified unanticipated cochlear fibrosis in 1 patient, vestibular schwannoma in 1 patient, and patency in the second turn of the cochlear in a patient with LO. The study also disproved cochlear fibrosis suspected on HRCT imaging in 1 patient. These findings suggest that, in addition to HRCT scans, high-resolution, T2-weighted MRI studies of the temporal bone may be useful preoperatively when considering candidates for cochlear implantation. However, the value of MRI in preoperative assessment of candidates for cochlear implantation is not universally accepted.
Histologic Findings: See Pathophysiology.

TREATMENT Section 5 of 8

Medical Care: Ceftazidime is a first-line agent for the prevention of otogenic and meningogenic labyrinthitis because it reaches higher concentrations in the perilymph and CSF than other CSF-penetrating agents (eg, cefuroxime, cefotaxime).

Steroids have been shown to inhibit the synthesis of connective tissues, impair the formation of granulation tissue, and decrease total collagen formation; however, these effects may be indirect sequelae of inflammatory suppression. Several human and animal studies have demonstrated that steroid-induced immunosuppression may reduce hearing loss associated with bacterial meningitis. Lebel et al found that treatment with dexamethasone caused a statistically significant reduction in subsequent hearing loss. This finding applied only to meningitis that was caused by H influenzae. The mechanism of effect of dexamethasone on meningitis is unknown, but it is hypothesized to result from inhibition of internal mediators of inflammation (eg, interleukin-1 [IL-1], cachectin, prostaglandins). "