Injection of doxorubicin into rabbit eyelid does not result in loss of facial motor neurons

In both laboratory and clinical studies, injection of doxorubicin directly into the eyelid results in permanent muscle loss of the majority of fibers within treated eyelids. A first clinical trial of this technique in blepharospasm and hemifacial spasm patients has been performed. All patients who completed a full course of doxorubicin treatment showed a permanent decrease in eyelid strength, with over 50% of these patients requiring no further treatment. Doxorubicin is known to be carried by retrograde axonal transport to the brain and is a known neurotoxin. This raises the question of the effect of these treatments on the facial neurons which innervate the orbicularis oculi muscle in the eyelids. The effect on the number of facial nuerons present after injection of doxorubicin into the eyelid of rabbits was determined using both HRP and diI retrograde labeling techniques. Despite the extensive and permanent muscle loss caused by the doxorubicin treatments, there was no measurable loss of facial neurons on the doxorubicin treated sides. DiI was shown to be myotoxic at high concentrations and amplified the myotoxic effect of doxorubicin. Lack of neuronal loss may offer assurance of clinical safety to the facial motor neurons of muscles spasm patients who receive doxorubicin injections into their eyelids.