Rapid Protein Test for Perilymph Fistula

The existence of a perilymph fistula may be difficult to prove preoperatively or at surgery, except in obvious cases in which perilymph can be seen coming out of the inner ear around the stapes footplate or round window niche. Some surgeons doubt the common occurrence of spontaneous perilymph fistula. Most surgeons believe that a perilymph fistula is rare and is produced by some type of trauma and pressure change to the inner ear fluids. Analysis of fluid collected from the oval window area and round window niche may be a great help in confirming or disproving the diagnosis of perilymph fistula. After a myringotomy or tympanotomy, fluid collected in micropipets from the oval window or round window area is analyzed for protein concentration, using rapid protein indicator paper. The original technique was developed in the 1960's to analyze the inner ear fluid as a diagnostic procedure (i.e., diagnostic labyrinthotomy) in acoustic neuroma suspects. Normal perilymph has a protein content of approximately 200 mg %, which turns the indicator paper light green, whereas serum or transudate has a protein content of approximately 7000 mg %, which turns the indicator paper dark green. The protein concentration is determined by comparing the color of the indicator paper with the color developed by known protein standards. A middle ear tap may help avoid negative middle ear exploration for perilymph fistula and helps document the presence or absence of perilymph after the exploration.