Chương 8

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CMDT 2013

8

Ear, Nose, & Throat Disorders Lawrence R. Lustig, MD, & Joshua S. Schindler, MD

DISEASES OF THE EAR HEARING LOSS

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E sse n t i a ls o f d i a g n o s i s

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Three main types of hearing loss: conductive, sensory, and neural.  Most commonly due to cerumen impaction, transient eustachian tube dysfunction associated with upper respiratory tract infection, or age-related hearing loss. 

``Classification & Epidemiology Table 8–1 categorizes hearing loss as normal, mild, moderate, severe, and profound and outlines the vocal equivalent as well as the decibel range.

A. Conductive Hearing Loss Conductive hearing loss results from dysfunction of the external or middle ear. There are four mechanisms, each resulting in impairment of the passage of sound vibrations to the inner ear: (1) obstruction (eg, cerumen impaction), (2) mass loading (eg, middle ear effusion), (3) stiffness effect (eg, otosclerosis), and (4) discontinuity (eg, ossicular disruption). Conductive losses in adults are most commonly due to cerumen impaction or transient eustachian tube dysfunction associated with upper respiratory tract infection. Persistent conductive losses usually result from chronic ear infection, trauma, or otosclerosis. Conductive hearing loss is often correctable with medical or surgical therapy—or in some cases both.

B. Sensory Hearing Loss Sensory and neural causes of hearing loss are difficult to differentiate due to testing methodology, thus often referred to as ‘sensorineural.’ Sensory hearing loss results

from deterioration of the cochlea, usually due to loss of hair cells from the organ of Corti. Sensorineural losses in adults are common. The most common form is a gradually progressive, predominantly high-frequency loss with advancing age (presbyacusis). Additional common causes include excessive noise exposure, head trauma, and systemic diseases. An individual’s genetic make-up influences all of these causes of hearing loss. Sensory hearing loss is usually not correctable with medical or surgical therapy but often may be prevented or stabilized. An exception is a sudden sensory hearing loss, which may respond to corticosteroids if delivered within several weeks of onset. Huang Q et al. Age-related hearing loss or presbyacusis. Eur Arch Otorhinolaryngol. 2010 Aug;267(8):1179–91. [PMID: 20464410] Rauch SD. Clinical practice. Idiopathic sudden sensorineural hearing loss. N Engl J Med. 2008 Aug 21;359(8):833–40. [PMID: 18716300] Rauch SD et al. Oral vs intratympanic corticosteroid therapy for idiopathic sudden sensorineural hearing loss: a randomized trial. JAMA. 2011 May 25;305(20):2071–9. [PMID: 21610239] Shearer AE et al. Deafness in the genomics era. Hear Res. 2011 Dec;282(1–2):1–9. [PMID: 22016077]

C. Neural Hearing Loss Neural hearing loss occurs with lesions involving the eighth nerve, auditory nuclei, ascending tracts, or auditory cortex. It is the least common clinically recognized cause of hearing loss. Causes include acoustic neuroma, multiple sclerosis, and auditory neuropathy. Manchaiah VK et al. The genetic basis of auditory neuropathy spectrum disorder (ANSD). Int J Pediatr Otorhinolaryngol. 2011 Feb;75(2):151–8. [PMID: 21176974]

``Evaluation of Hearing (Audiology) In a quiet room, the hearing level may be estimated by having the patient repeat aloud words presented in a soft whisper, a normal spoken voice, or a shout. A 512-Hz tuning fork is useful in differentiating conductive from


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