Composition of the otosclerotic stapes: electron microprobe analyses.

For the first time, otosclerotic stapes have been distinguished from unafflicted controls at a high level of significance by using a spectrum of elements measured by energy-dispersive spectrometer-electron probe microanalyses (EDS/EPMA). Discriminant analyses of the maximum concentration of 13 elements measured at several sites within each of 32 stapes differentiated otosclerotic from unafflicted individuals well above the 95% confidence level. Eight of the 9 control (unafflicted) and 21 of the 23 afflicted stapes were correctly classified. In descending order of contribution to the discriminant function, the elements are Zn > Cr > K > Ca > Si > Mn > Na > Al > Mg > P > Fe > S > Ti. Zinc and chromium account for much of the difference, but discriminant analyses excluding them still distinguish the two groups at the 95% confidence level. These results are consistent with previous reports of high levels of alkaline phosphatase, a zinc-containing enzyme, in afflicted stapes. But the broad spectrum of elements capable of distinguishing otosclerotic stapes warrants study of additional zinc-containing and other metal-containing or metal-activated moieties.