P0 antigen detection in sudden hearing loss and Ménière's disease: a new diagnostic marker?

OBJECTIVE To evaluate the presence of IgG autoantibodies against the P0 antigen in patients affected by sudden hearing loss and Meniere's disease (MD). MATERIAL AND METHODS All patients underwent a tonal audiometric evaluation, tympanometry, evaluation of the stapedial reflex threshold with decay time, determination of auditory brainstem responses and a complete vestibular assessment involving evaluation of spontaneous and positional nystagmus (Frenzel glasses), a head thrust test and a caloric test (Fitzgerald-Hallpike technique). Blood samples were drawn from all patients for the immunologic assessment of IgG antibodies against the P0 antigen (30-kDa protein) of guinea pig inner ear extracts using a Western blot assay. RESULTS Ten patients affected by sudden hearing loss showed specific IgG antibodies against the P0 protein. Specifically, the P0 positive band was detectable in 5/45 patients with unilateral auditory impairment and in 5/5 of those with bilateral forms of auditory impairment. Among MD patients, the P0 positive band was detectable only in those with bilateral audiovestibular impairment (n = 10). Interestingly, in none of the 35 patients affected by monolateral MD were specific IgG antibodies against the P0 protein detectable. CONCLUSION The positive reactions to P0 in all bilateral MD and bilateral sudden hearing loss patients found in this study strongly indicate that these pathologies are the result of an ongoing autoimmune process directed against specific antigens of the inner ear.