Tinnitus: types, differential and investigation

What it is

Tinnitus divides first into subjective and objective. Subjective tinnitus can only be heard by the patient, is not audible to an observer, and is usually caused by abnormal nerve activity in the audiotary cortex. Objective tinnitus can be heard by the examiner and is caused by paraauditory structures.

Causes and risk

Subjective tinnitus is the tinnitus of presbyacusis, noise induced loss, ototoxic drugs and Ménière's disease. Objective tinnitus is the tinnitus of glomus jugulare, insects such as maggots, the temporomandibular joint, palatal causes, AV malformations or aneurysms, and carotid body tumours.

Sensorineural hearing loss is the most common identified cause, although tinnitus is idiopathic; otologic, vascular, neoplastic, neurologic, pharmacologic, dental and psychological factors are listed as well. Several medications can cause tinnitus, but allopurinol is not one of them.

• Presbycusis is sensorineural hearing loss associated with aging, starting in the 5th and 6th decades. Tinnitus comes with progressive bilateral hearing loss, initially at high frequencies and then middle, loss of discrimination of speech against background noise so that people are described as mumbling, and the recruitment phenomenon, an inability to tolerate loud sounds.
• Noise induced sensorineural hearing loss follows 85-90 dB over months or years, or a single sound greater than 135 dB. Exposure to loud sound gives decreased sensitivity or an increased threshold for sound, with or without aural fullness and tinnitus; when the noise is removed hearing returns to normal in the temporary form, while in the permanent form hearing does not return to the previous state.
• Aspirin in large doses is generally reversible. Aminoglycosides cause irreversible destruction of the outer hair cells in the organ of Corti, with hearing loss initially on the highest frequencies, tinnitus and vertigo worse in the dark; the risk is greater with large doses, high blood levels, long duration of therapy, in the elderly and with preexisting hearing impairment, and treatment is to stop the aminoglycosides immediately. Antimalarials, that is quinines, give hearing loss with tinnitus that is reversible if discontinued but can lead to permanent loss.