[The "Muenster classification" of high frequency hearing loss following cisplatin chemotherapy]

Slight high frequency hearing loss following cisplatin chemotherapy can be proof of an ototoxic effect even when hearing ability is not yet clinically affected. To answer scientific questions, such as the relationship between cisplatin ototoxicity and drug regime or individual tolerance, early detection of ototoxicity and a classification relating to intensity and the affected frequencies are required. A search for relevant literature resulted the WHO-classification (1991) describing clinically relevant hearing loss and two high frequency hearing loss classifications published by Khan et al. (1982) and Brock et al. (1991). Their application is compared to a new, proprietary classification.

55 patients (32 boys, 23 girls) undergoing cisplatin chemotherapy at Muenster University Hospital from 1999 to 2004 underwent audiometric tests in our department. From this data we developed a grading system, that was based on the WHO classification, but paid special attention to early ototoxic effects, to intensity of hearing loss and to the frequencies affected: Grade 0 (normal hearing) includes hearing loss of not more than 10 dB in all frequencies. Grade 1 (beginning hearing loss) encompasses > 10 dB up to 20 dB in at least one frequency or tinnitus. Grade 2 (moderate impairment) describes hearing loss > or = 4 kHz and differentiates 2a (> 20 to 40 dB), 2b (> 40 to 60 dB) and 2c (> 60 dB). Hearing loss < 4 kHz > 20 dB in grade 3 (severe impairment, hearing aids needed) is further classified according to grade 2 in a, b and c. Grade 4 (loss of function) finally describes average hearing loss < 4 kHz of at least 80 dB. This classification is compared to the two high frequency hearing loss classifications (Khan et al. and Brock et al.).

The Muenster classification, compared to Khan et al. and Brock et al., demonstrated the best results in the early detection of hearing loss: All children with hearing loss of at least 20 dB after therapy had already shown pathological audiograms during treatment, when those audiograms were assessed by our classification. All children whose audiograms were flagged as pathological by our classification finally developed hearing loss. In terms of the prediction of hearing loss, our classification evaluated processing audiograms with a sensitivity, specificity and efficiency of 1.0. Progressive hearing loss was detected in 45 patients (Khan et al. 30, Brock et al. 38). Therefore our classification showed a better suitability for monitoring hearing loss than the other classifications.

The Muenster classification is a suitable new basis for scientific questions concerning cisplatin ototoxicity. It detects hearing loss earlier and maps progression of hearing loss more precisely than the existing high frequency classifications (Khan et al. and Brock et al.).