Tinnitus and treatment-resistant depression

Tinnitus, a frequent disorder, is the conscious perception of a sound in the absence of a corresponding external acoustic sound source in the sense of a phantom sound. Although the majority of people who perceive a tinnitus sound can cope with it and are only minimaly impaired in their quality of lfe, 2-3% of the population perceive tinnitus as a major problem. Recently it has been proposed that the two groups should be differentiated by distict terms: "Tinnitus" describes the auditory or sensory component, whereas "Tinnitus Disorder" reflects the auditory component and the associated suffering. There is overwhelming evidence that a high tinnitus burden is associated with the increased occurrence of comorbidities, including depression. Since no causal therapeutic options are available for patients with tinnitus at the present time, the identification and adequate treatment of relevant comorbidities is of great importance for the reduction of tinnitus distress. This chapter deals with the relationship between tinnitus and depression. The neuronal mechanisms underlying tinnitus will first be discussed. There will also be an overview about depression and treatment resistant depression (TRD). A comprehensive review about the state-of-the-art evidences of the relationship between tinnitus and TRD will then be provided.