Free amino acid analysis of guinea pig perilymph: a possible clinical assay for the PLF enigma?

Abstract

Controversy prevails regarding the accuracy of the clinical diagnosis of perilymphatic fistula (PLF). The diagnosis of PLF has been based on the subjective evaluation of vestibular function tests and the intraoperative macroscopic visualization of "clear fluid" from the oval/round windows at the time of exploratory tympanotomy. However, the subjective visual characterization of PLF varies among observing surgeons. Furthermore, perilymph can be "contaminated" with serum, blood, cerebrospinal fluid (CSF), and local anesthesia. This article presents a scientific biochemical microassay for the free amino acid profile of perilymph. Microaliquots of uncontaminated perilymph were sampled from the bilateral round windows (scala tympani) of 20 guinea pigs and analyzed for 19 free amino acid concentrations (FAAC) by high-performance liquid chromatography (HPLC). These samples were compared with the FAAC of guinea pig serum samples. Perfect predictor value ranges were nonoverlapping for 12 of 19 free amino acids in perilymph vs. plasma. Amino acid microassay of middle ear fluid for verification of "true" perilymph vs. nonperilymph fluids by the identification of nonoverlapping FAA markers may allow scientific verification of the existence of PLF in "suspected" patients.