Experimental trigeminal glycerol injection. Electrophysiologic and morphologic effects.

The mechanism by which glycerol abolishes the pain of tic douloureux with minimal trigeminal deafferentation remains unknown. To study the action of glycerol, ten cats underwent unilateral retrogasserian injection of anhydrous glycerol. The contralateral (control) side was injected with saline. Glycerol injection increased the average latencies and reduced the average amplitudes of trigeminal brain-stem evoked potentials. Histopathologic examination disclosed focal demyelination, axonal swelling, endoneurial fibrosis, and neuronal loss. Evoked potentials were severely altered or abolished in cats with axonal damage in the maxillary portion of the postganglionic nerve. Glycerol injection into the trigeminal nerve damages axons and myelin sheaths. We believe that relief of tic douloureux after glycerol injection most likely results from further destruction of the abnormally myelinated fibers implicated in the etiology of trigeminal neuralgia.