Tinnitus: An Unrecognised Symptom of Functional Neurological Disorder

Background Functional neurological disorder (FND) is a common neurological condition characterised by symptoms which vary characteristically with attention. In the sensory realm, these symptoms frequently take the form of 'phantom' perception in the absence of sensation. While the condition is generally regarded not to cause auditory symptoms, tinnitus is a phantom perception which varies with symptom-focused attention, and is suggested to have similar underlying mechanisms to those proposed for FND. Based on this, we hypothesized that tinnitus might reflect the same underlying process as FND, and that it would therefore be more common in people with FND (pwFND). Methods Using an international database, we compared the proportions of pwFND who reported tinnitus with a control group. To ensure that observed differences were not attributable to agreement bias in symptom reporting, we also conducted an experiment where pwFND and controls were asked to report which symptoms they had experienced in the past month, 14 of which were symptoms of FND, and 7 of which were unrelated. Results Rates of tinnitus were significantly higher in the FND group (54% HDI 50 - 57%, n=732) than the control group (17% HDI 8.5 - 25%, n=59). In the symptom reporting experiment, pwFND (n=38) reported more FND-related symptoms than controls (n=38), but there was no between-group difference in reporting of non-FND related symptoms. Discussion Based on the markedly higher prevalence of tinnitus in pwFND than controls, and the substantial overlap in mechanisms and phenomenology, we believe tinnitus should be considered a possible symptom of FND, where both conditions reflect a failure of symptom resolution after incitement by a peripheral stimulus.