Tinnitus: Characteristics, Causes, Mechanisms, and Treatments

Tinnitus-the perception of sound in the absence of an actual external sound-represents a symptom of an underlying condition rather than a single disease. Several theories have been proposed to explain the mechanisms underlying tinnitus. Tinnitus generators are theoretically located in the auditory pathway, and such generators and various mechanisms occurring in the peripheral auditory system have been explained in terms of spontaneous otoacoustic emissions, edge theory, and discordant theory. Those present in the central auditory system have been explained in terms of the dorsal cochlear nucleus, the auditory plasticity theory, the crosstalk theory, the somatosensory system, and the limbic and autonomic nervous systems. Treatments for tinnitus include pharmacotherapy, cognitive and behavioral therapy, sound therapy, music therapy, tinnitus retraining therapy, massage and stretching, and electrical suppression. This paper reviews the characteristics, causes, mechanisms, and treatments of tinnitus.

A Case with Viral Encephalitis presenting a Dissociations in the Retrograde Amnesia

We describe a case of anterograde and retrograde amnesia resulting from probable herpes simplex encephalitis. In retrograde amnesia, dissociations not only between episodic and semantic memories, but also between semantic memories for personal and public things were observed. We postulated, using FDG-PET, that the former was caused by mesial temporal lesions, based on `multiple trace theory', and the latter, by bilateral lateral temporal lesions, which were probably related to the retrieval of semantic memory, especially for public things.

Neuropsychology and PET Findings of Corticobasal Degeneration

BACKGROUND: Corticobasal degeneration (CBD) is a rare neurodegenerative disorder involving the cortical and subcortical areas enabling it to cause abnormalities of both cognition and movement. In some reports, CBD has been known to develop variable degrees of intellectual, memory and language impairment. However, detailed neuropsychological assessments of CBD up to now have been few. We conducted a detailed neuropsychological investigation and FDG-PET to delineate the pattern of neuropsychological dysfunction of CBD and to correlate neuropsychological dysfunction with FDG-PET findings. METHODS: All 6 patients (5; right handedness, 1; left handedness) were diagnosed with CBD using clinical criteria. All the patients underwent detailed neuropsychological and brain FDG-PET tests. RESULTS: Neuropsychological tests showed multiple cognitive dysfunctions with moderate memory impairment. FDG-PET scans showed asymmetric decreased metabolism in bilateral fronoto-temporo-parietal cortical and subcortical areas. The extent of asymmetricity was greater on the subcortical than cortical areas. Unlike previous reports, the medial temporal and fronto-parietal metabolisms were similarly depressed. CONCLUSIONS: All CBD patients displayed prominent deficits on mostly cognitive domains. FDG-PET may explain the relation between cognitive dysfunctions and cortical hypometabolism and help differentiate CBD with other dementing disorders.

Subtypes and Their Clinical Characteristics of Mild Cognitive Impairment (MCI): Cross Sectional Study

BACKGROUND: Mild cognitive impairment (MCI) represents a transitional state between the cognitive changes of normal aging and very early dementia. Recently, the published MCI classification in `The Current Concepts in MCI Conference' suggested subtypes of MCI (amnestic, single nonmemory domain, multiple domains slightly impared) based on recognized heterogeneity. The purpose of this study was to ascertain the existence of subtypes of MCI and investigate their relative prevalence and clinical characteristics. METHODS: We recruited the MCI patients according to the consensus criteria of MCI. We classified them into 3 subtypes of MCI by our working criteria based on the definitions of MCI subtypes and then calculated their respective prevalence. We described their various clinical variables including demographic features, symptoms on the first visit, neuroimaging findings, and the genotype of apolipoprotein E. RESULTS: Sixty patients (36 females and 24 males) were enrolled as MCI and analyzed. The prevalence of each subtype (amnestic, single nonmemory domain, multiple domains slightly impared) were 13 (21.67%), 24 (40.0%), and 23 (38.33%) respectively, suggesting the most prevalent type was the single nonmemory domain type. MCI cases with subcortical vascular features were 18 (11 single nonmemory domain and 7 multiple domains slightly impaired). The ApoE epsilon4 carriers were about 50% of tested patients. CONCLUSIONS: We ascertained the existence of MCI subtypes and investigated their prevalence and various clinical features. In evaluation of MCI patients, we should keep the notion of heterogeneity and subclassification in mind.