Despite being a common condition that affects nearly 15% of the population, and despite much research progress made in the recent years, tinnitus remains a scientific and clinical enigma.Subjective tinnitus is defined as a phantom perception of a tone or noise in the absence of any physical source. It is known to be a heterogeneous condition,both in the way of manifestation and of generation. In general, “heterogeneity” describes the fact that there is a non-uniform appearance of a substance, organism, or disease. Whenever there is a non-uniformity in at least one quality, we can call it “heterogeneous.” Tinnitus patients differ on at least four dimensions:First, tinnitus patients may present diverse clinical profiles with respect to the perception of tinnitus (e.g., laterality of tinnitus, tinnitus pitch, ringing, buzzing, hissing, or cricket sounds). Additionally, tinnitus can be occasional or permanent, acute or chronic, pulsatile, or constant.Second, while there are multiple ways of perceiving tinnitus,it is also associated with multiple causal risk factors—hearing loss, temporomandibular joint disorder, and aging being among the most common ones. There are also numerous related comorbidities that add to the complex clinical picture of tinnitus (e.g., hyperacusis, depression,sleep disorders, headache, concentration problems). A third dimension is the associated tinnitus distress,the psychological reaction to the ongoing tinnitus perception; it can differ largely among patients. Fourth, there is a large variation of treatment responses of the tinnitus patients
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- Animal model