Childhood myasthenia

Myasthenia mimicking monocular elevation deficiency

Monocular elevation deficiency is the inability to elevate the eye in abduction and adduction. Myasthenia gravis could mimic any pattern of ophthalmoplegia. However, myasthenia gravis mimicking monocular elevation deficiency appears to be very rare. A 12-month-old girl presented with the inability to elevate the left eye and blepharoptosis from 3 months of age. A neostigmine test showed a weakly positive response. Repetitive stimulation of the left orbicularis oculi produced no decremental response. Three assays for acetylcholine receptor antibodies were negative. Placing ice over the lids definitely improved left blepharoptosis. In conclusion, myasthenia gravis could mimic elevation deficiency. An ice test could be very helpful in making the diagnosis. Myasthenia gravis should be included in the differential diagnosis of monocular elevation deficiency even at a young age.

Childhood ocular myasthenia gravis

PURPOSE

To investigate the clinical manifestations and ocular findings in children with ocular myasthenia gravis (MG) that rarely have been reported in the literature.

DESIGN

Retrospective, noncomparative case series.

PARTICIPANTS

Twenty-four consecutive patients less than 15 years of age with ocular MG treated between June 1988 and July 2001.

METHODS

The medical records of 6 boys and 18 girls with ocular MG were reviewed retrospectively.

MAIN OUTCOME MEASURES

Alternate prism cover and uncover test, examination of ductions and versions, and visual acuity.

RESULTS

Mean age at onset was 38 months. Ptosis was found in 23 patients (96%), strabismus in 21 patients (88%), and amblyopia in 5 patients (21%). Exotropia combined with vertical heterotropia was the most frequent type of strabismus. Ductions were limited in 17 patients (71%), among whom supraduction or infraduction limitations were most frequently observed. Contrary to previous reports, medial rectus underaction was less common than lateral rectus underaction. Manifestations of strabismus and limitation of duction were variable and changed frequently during the follow-up period. The combined use of prednisone and pyridostigmine was found to be the predominant form of maintenance therapy, and ptosis was more responsive to drug therapy than limited ocular motility.

CONCLUSIONS

Children with ocular MG were found to have a high incidence of ptosis (96%) and exotropia and vertical hyperdeviation. Limitation on adduction was less common than that on abduction. First reported incidence of amblyopia (21%) and a relative nonresponsiveness of the limitation of eye movement to treatment were also noted.