Sudden bilateral hearing loss and sporadic mitochondrial DNA deletion

Several studies have indicated that a number of different mitochondrial DNA (mtDNA) mutations may be responsible for human pathologies. Sensorineural Hearing Loss (SNHL) may be associated with known syndromes (syndromal SNHL) or represent the only manifestation of mitochondrial damage (non-syndromal hearing loss). Moreover, mtDNA alterations may be responsible for aminogly coside-induced deafness. We describe a patient harbouring a single sporadic mtDNA deletion, who pres ented with sudden adult-onset bilateral, although non-simultaneous SNHL, th at was partially responsive to corticosteroids. Increased values of rest, a nd exercise, blood lactic acid were decisive for diagnosis, prompting muscl e biopsy that revealed the mtDNA deletion. The case underscores the importa nce of investigating a mitochondrial disease in cases of SNHL of unknown or igin and points out the importance of an increased blood level of lactic ac id as a screening test.