Crocodile tears and thread test of lacrimation

Patients with incomplete recovery from peripheral facial paralysis often complain of eye-watering while eating (crocodile tears or gustolacrimal reflex). In 55 patients (22 completely recovered from peripheral facial paralysis, 23 incompletely recovered, and ten with hemifacial spasm), lacrimation was monitored by the thread test (a modification of the Schirmer test) during taste stimulation. In the 22 patients with complete recovery, the results of the thread test did not differ before and after a sweet-sour candy was given (taste stimulation). All the patients with incomplete recovery showed either synkinesis or contracture. Lacrimation on the side of the lesion was high even before taste stimulation. After taste stimulation, a rapid and definite increase in lacrimation was observed. The results show that in patients with synkinesis and incomplete recovery after peripheral facial paralysis, the misdirected regeneration of the injured nerve fiber often occurs from the gustatory nerve to the lacrimal nerve, as well as between motor fibers.