A comparison of the severity of tinnitus in patients with and without hearing loss using the tinnitus functional index (TFI)

One third of all adults report experiencing tinnitus at some time in their lives. Ten percent to 15% have prolonged tinnitus requiring medical evaluation. Classification of tinnitus requires a thorough history and physical examination, supplemented by appropriate diagnostic tests. Tinnitus can be categorized according to its qualities (as described by the patient and matched on the audiometer) and its clinical type (as suggested by probable etiology). Audiologic testing, tinnitus analysis, and occasional radiologic studies assist with classification and direction of treatment planning. The THI is another method of classification that can facilitate the precise monitoring of a patient's progress. By using these tools and standardizing the language, tinnitus studies around the world can become more comparable and patients can be better monitored for treatment response.

Chronic subjective tinnitus is a prevalent condition that causes significant distress to millions of Americans. Effective tinnitus treatments are urgently needed, but evaluating them is hampered by the lack of standardized measures that are validated for both intake assessment and evaluation of treatment outcomes. This work was designed to develop a new self-report questionnaire, the Tinnitus Functional Index (TFI), that would have documented validity both for scaling the severity and negative impact of tinnitus for use in intake assessment and for measuring treatment-related changes in tinnitus (responsiveness) and that would provide comprehensive coverage of multiple tinnitus severity domains. To use preexisting knowledge concerning tinnitus-related problems, an Item Selection Panel (17 expert judges) surveyed the content (175 items) of nine widely used tinnitus questionnaires. From those items, the Panel identified 13 separate domains of tinnitus distress and selected 70 items most likely to be responsive to treatment effects. Eliminating redundant items while retaining good content validity and adding new items to achieve the recommended minimum of 3 to 4 items per domain yielded 43 items, which were then used for constructing TFI Prototype 1.Prototype 1 was tested at five clinics. The 326 participants included consecutive patients receiving tinnitus treatment who provided informed consent-constituting a convenience sample. Construct validity of Prototype 1 as an outcome measure was evaluated by measuring responsiveness of the overall scale and its individual items at 3 and 6 mo follow-up with 65 and 42 participants, respectively. Using a predetermined list of criteria, the 30 best-functioning items were selected for constructing TFI Prototype 2.Prototype 2 was tested at four clinics with 347 participants, including 155 and 86 who provided 3 and 6 mo follow-up data, respectively. Analyses were the same as for Prototype 1. Results were used to select the 25 best-functioning items for the final TFI. Both prototypes and the final TFI displayed strong measurement properties, with few missing data, high validity for scaling of tinnitus severity, and good reliability. All TFI versions exhibited the same eight factors characterizing tinnitus severity and negative impact. Responsiveness, evaluated by computing effect sizes for responses at follow-up, was satisfactory in all TFI versions.In the final TFI, Cronbach's alpha was 0.97 and test-retest reliability 0.78. Convergent validity (r = 0.86 with Tinnitus Handicap Inventory [THI]; r = 0.75 with Visual Analog Scale [VAS]) and discriminant validity (r = 0.56 with Beck Depression Inventory-Primary Care [BDI-PC]) were good. The final TFI was successful at detecting improvement from the initial clinic visit to 3 mo with moderate to large effect sizes and from initial to 6 mo with large effect sizes. Effect sizes for the TFI were generally larger than those obtained for the VAS and THI. After careful evaluation, a 13-point reduction was considered a preliminary criterion for meaningful reduction in TFI outcome scores. The TFI should be useful in both clinical and research settings because of its responsiveness to treatment-related change, validity for scaling the overall severity of tinnitus, and comprehensive coverage of multiple domains of tinnitus severity.

Depressive symptoms are common in individuals with tinnitus and may substantially aggravate their distress. The mechanisms, however, by which depression and tinnitus mutually interact are still not fully understood. Here we review neurobiological knowledge relevant for the interplay between depression and tinnitus. Neuroimaging studies confirm the existence of neural circuits that are activated both in depression and tinnitus. Studies of neuroendocrine function demonstrate alterations of the HPA-axis in depression and, more recently, in tinnitus. Studies addressing neurotransmission suggest that the dorsal cochlear nucleus that is typically hyperactive in tinnitus, is also involved in the control of attention and emotional responses via projections to the locus coeruleus, the reticular formation and the raphe nuclei. Impaired hippocampal neurogenesis has been documented in animals with tinnitus after noise trauma, as in animal models of depression. Finally, from investigations of human candidate genes, there is some evidence to suggest that variant BDNF may act as a common susceptibility factor in both disorders. These parallels in the pathophysiology of tinnitus and depression argue against comorbidity by chance and against depression as pure reaction on tinnitus. Instead, they stand for a complex interplay between tinnitus and depression. Implications for tinnitus treatment are discussed.