Assessment of tympanometry in abnormalities of the tympanic membrane

Isolated abnormalities of the tympanic membrane have been postulated to affect tympanometry. The authors tested 33 abnormal tympanic membranes in 19 patients with tympanosclerosis and/or thin membranes (having no middle or fibrous layer) against a control group of 32 normal ears in 16 age- and sex-matched patients. All selected patients were free of middle ear disease on the basis of normal hearing, normal pneumatic otoscopic findings, and the presence of crossed acoustic reflexes or normal findings at paracentesis. All patients in the control group had normal type A tympanograms, while 20 (61 per cent) of the tympanic membranes in the experimental group produced abnormal tympanograms. Of the 20 abnormal tympanic membranes, 35 per cent were type A_s, 35 per cent were type A_d, 5 per cent were type B, and 25 per cent were type C. The tympanosclerotic membranes were more likely to have increased stiffness on the tympanogram, such as A_s, or B, while the thin membranes had an A_d configuration. The greater the extent of the abnormality within the tympanic membrane, the more abnormal was the tympanogram. This study has demonstrated that isolated abnormalities of the tympanic membrane, such as tympanosclerosis and thin membranes, can alter the tympanogram in the absence of middle ear disease, and that the type of tympanogram can be predicted from the nature and extent of the abnormality. Therefore, an abnormal tympanogram may indicate middle ear disease, abnormality of the tympanic membrane, or both. The presence of an acoustic reflex is important in this differentiation.