ELECTROMYOGRAPHIC FEATURES OF LEVATOR PALPEBRAE SUPERIORIS AND ORBICULARIS OCULI MUSCLES IN BLEPHAROSPASM

Electromyographic (EMG) recording war; performed synchronously from th e levator palpebrae superioris (LP) and the orbicularis oculi (OO) mus cles in 28 patients referred to us for treatment of blepharospasm with botulinum A toxin. At the time of this study, 19 patients were under the treatment with botulinum, four starred treatment shortly after the EMG recording and five patients had not yet been treated. Based on th e EMG patterns, we were able to classify five majorgroups of abnormali ties. Group 1 (blepharospasm): consisted of to patients with dystonic discharges limited to OO, normal LP tonic activity, intact reciprocal inhibition between LP and OO and dense bursts of action potentials wit h high amplitude preceding the return of LP tonic activity, i.e. 'post inhibition potentiation ' of LP, brought about by a brief contraction of OO. Group 2 (combined dystonic activities of LP and OO): seven pati ents belonged to this group. The EMG recording revealed alternating tr emulous discharges in both LP and OO muscles, and short intervals of c o-contractions due to moderately disturbed reciprocal inhibition. Grou p 3 (combination of blepharospasm, LP motor impersistence): the EMG pa tterns, observed in three patients, were characterized by a gradual ce ssation of LP activity, followed by a brief contraction of OO, which f acilitated the return of LP activity, resulting in opening of the eyes . The EMG recordings, thus, revealed the crucial, beneficial role of p ostinhibition potentiation as a compensatory mechanism in this type of eyelid movement disorder. The EMG patterns were also characterized by short or;prolonged periods of dystonic discharges limited to the OO m uscles. Group 4 (combination of blepharospasm, involuntary LP inhibiti on): this group consisted of four patients. In addition to episodes of dystonic activities of OO, the EMG also showed some periods of involu ntary inhibition of LP without any concomitant activities of OO. Two p atients also exhibited a failure of inhibition of OO muscle activity, following the voluntary contraction of this muscle. The postinhibition potentiation was often not observed Group 5 (involuntary LP inhibitio n): consisted of four patients with EMG patterns of involuntary inhibi tion of LP activity, without any dystonic discharges in OO. The postin hibition potentiation was not observed in this group. The response to the treatment with botulinum toxin was good in the first group and gra dually worsened towards the fifth group. Application of botulinum into multiple sites of OO, especially its pretarsal portion, resulted in b etter response to the treatment in the second and fourth groups. We co nclude that synchronous EMG recording of LP and OO is an indispensable investigation method to establish the origin of varying forms of eyel id movement disorders in patients with clinical symptoms of blepharosp asm, and to analyse the cause of unsatisfactory response to the treatm ent with botulinum.