SDL 18: Otosclerosis

Otosclerosis (vague def.) Abnormal bone growth around the stapes (specific def.) Genetically-mediated metabolic bone disorder…involving the temporal bone 1st-fibrous ankylosis of the stapes footplate 2nd-bony outgrowth, fixing stapes to the cochlear oval window Therefore, stapes cannot vibrate like normal…hence loss of hearing Progressive conductive hearing loss (typical) Can involve other portions of the cochlea and actually result in sensorineural hearing loss as well. Also says annular ligament becomes ossified to the surrounding bone (otic capsule)

Otosclerosis Typically pts present w/ slowly progressive hearing loss. Annular ligament is ossified to the otic capsule. Main point is that the STAPES CANNOT VIBRATE like normal! Therefore, we can’t hear as we normally would Prego women experience rapid decrease in hearing. Typically pts present w/ slowly progressive hearing loss. Pts usually in 20s when this starts. Can begin 15-45 yo though.

Genetics and Epidemiology 1 parent has it: offspring 25% Both parents have it: offspring 50% Caucasians. Not sex-linked, women are twice as likely to go see a doc about it though Affects both ears in most cases Most studies conclude auto dom with incomplete penetrance

IgG Viral etiology Measles! Supporting evidence: Nucleocapsids Nucleocapsids similar to measles found in otosc. osteoblasts Elevated IgG against measles found in perilymph Less occurrence after measles vaccine Now otosclerosis is classified as organ-specific to measles virus. Nucleocapsids Weasels virus! (measles) IgG

Pathophys Some studies show this is just a process of bone remodeling that affects the otic capsule Normally, bone remodeling does not occur in the otic capsule Bone remodeling depends directly on cytokines: OPG, RANK & RANKL OPG competes with RANK for the RANKL receptor on osteoblasts…thus, competitive inhibition Normally, we have type I fibrocytes producing very high levels of OPG in the otic capsule

Some Mouse Study.. Knocked out OPG in mice and guess what…they experienced symptoms similar to pts with otosclerosis. Active remodeling in otic capsule Histology: shows early signs of otosclerosis A: Active otosclerotic lesion involving the complete stapes footplate. Hypercellularity, several osteoclasts and osteolytic lacunae can be observed B: Larger magnification view of the previous section. The white arrow indicates a multinucleated osteoclast performing active osteolysis. Lamellar and woven patterns of cement lines is marked by black arrow C: Polarized light microscopic view of the previous section. The woven structure of cement lines can be well identified (black arrow). An osteoprotegerin-specific RT-PCR gave negative result. Housekeeping control RT-PCR was positive.

More Pathophys Osteosclerosis replaces normal bone with dense, sclerotic bone Two histologic phases: 1. Osteospongiotic phase 2. Osteosclerotic phase Osteospongiotic phase. This osteospongiotic phase can lead to a Schwartze sign. See later. Bone resorption around existing vessels

Otosclerotic Phase Resorbed bone is replaced with dense bone with few blood vessels Osteospongiotic lesion Osteosclerotic lesion O: Osteoslerotic bone N: normal bone

More Pathophys 80-90% of pts have lesions of the anterior oval window & calcification of the annular ligament or involvement of the stapes (old news) 8% lesions will involve cochlea and other parts of the labyrinth  sensorineural hearing loss. 2% will have both ossicular chain involvement and labyrinth So, a combination of the normal 80-90% and the rare 8% with labyrinth involvement

Clinical Presentation Principal symptoms: gradual hearing loss and tinnitus Pts first notice they can’t hear low-pitch sounds or whispers Can also have issues with tinnitus, balance, dizziness Dizziness/balance ? Progressive Low freq. whispers Tinnitus!

Physical Exam Eardrum is not like otitis media, looks pretty normal except!... 10% of patients will have a Scwhartze sign Reddish blue hue over promontory and oval Windows Rich vascular supply and Immature bone present too This pt had conductive hearing loss. Remember, the Schwartze sign is from the osteospongiotic phase, where bone resorption occurred around existing vessels

Diagnosis Conductive hearing loss: Inability to hear low frequencies Bc tones cannot reach the inner ear. (think of some kind of physical obstruction, rather than a neural problem) ENT physicians deal with these dudes. Pure Tone Audiometry is used to measure hearing sensitivity. It produces an audiograph-which plots intensity as a function of frequency

Exciting Exciting Audiograms.. Just the chart setup.

Normal Hearing

Conductive Hearing Loss Hear through bone normally, not thru air At least 10dB variance Probably going to hear high frequencies better than low Once again, the issue is transmitting sound waves from the outer ear, tympanic membrane, or inner ear ossicles (ossicle chain) Think physical obstruction issue.

Mixed Hearing Loss Bone conduction and air conduction are depressed But, bone conduction is usually better than air The difference bt the two thresholds is the air-bone gap

Sensorineural Loss Both poor air and poor bone conduction thresholds. NO air-bone gap! They are within 10dB of each other Now, thinking of nerve issues, brain processing, etc. Not some simple physical obstruction.

Imaging and Prognosis Could order a CT scan to view the stapes bound to the oval window of the cochlea BUT, it can be very hard to detect such a small issue…so, a neg CT does not rule out otosclerosis Prognosis Usually deteriorates until 45-50 yo. Then stabilizes. Very good prognosis with stapedectomy by ENT physicians. They remove immobilized stapes and replace with a prosthetic. Almost all patients have increased hearing and can fix tinnitus as well. stapedectomy