Ocular myasthenia with both AChR and MuSK antibodies

Case Report: We report a 15-year-old, previously healthy girl, who presented with a 5-month history of recurrent bilateral abducens paresis and unilateral ptosis. Two previous episodes had spontaneously resolved. Retrospectively, the girl had experienced a single short episode of dysphagia. In addition, she complained of moderate fatigue. Results of further ophthalmologic investigations, cerebral imaging, and cerebrospinal fluid (CSF) analysis were normal. Despite normal EMG findings, we suspected myasthenia and performed AChR and MuSK antibodies testing, both of which were significantly increased. The bedside Tensilon test was positive. There was no evidence of a thymoma or other neoplasia.

Under treatment with pyridostigmine, paresthesia and muscular fasciculation occurred, while no significant improvement of ocular symptoms could be observed. In addition, the patient now suffered from severe fatigue and slept approximately 17 hours per day. Although the AChR antibodies became negative, the patient was still significantly seropositive for MuSK antibodies. We therefore terminated the pyridostigmine therapy and initiated treatment with hydrocortisone and azathioprine.

Discussion: Here, we describe the fifth case of myasthenia with both AChR and MuSK antibodies. Similar to previously reported cases, our patient was AChR antibody positive at onset and subsequently became seronegative. Although this has been associated by other authors with thymectomy, our case illustrates that this phenomenon can occur indecently. Prevalence and pathogenesis of a co-occurrence of both antibodies remain to be elucidated. Usually antibody testing is performed in a step-by-step fashion, starting with the detection of AChR antibodies. A simultaneous determination of both antibodies in patients with myasthenia may contribute to further understanding.