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Myasthenia gravis is usually a chronic disorder, although remission rates of 25–30% can be expected with judicious interventions such as thymectomy and immunosuppression in appropriate cases. Spontaneous remission occurs rarely. Oosterhuis found a remission rate of only 1% per annum over 17 years among 180 patients with generalised myasthenia gravis treated with anticholinesterases alone.1 We describe a case of ocular and bulbar myasthenia in which there was complete recovery over a matter of weeks without immunosuppressive agents.
The patient, a 78 year old woman, developed acute, painless left sided ptosis in October 2002, while on holiday abroad. There was no diplopia. She had developed hypothyroidism one year before but was euthyroid on replacement therapy. The ptosis resolved gradually over the next few days. There was no family history of autoimmune diseases. Two weeks later she found she could not chew properly towards the end of a meal. The jaw weakness recovered the following day but later recurred, to the extent that she had to support her jaw while talking and eating. She had slight dysphagia but there was no history of choking, breathing problems, or limb weakness.
On examination in January 2003, there was no definite ptosis or ophthalmoparesis. No fatigability was demonstrated in the eyelids, and no weakness or fatigability was detected on testing jaw opening against resistance, although her jaw hung slackly open if not supported. Limb power and reflexes were normal.
Acetylcholine receptor antibodies (AchR-abs) were strongly positive at 11 nmol/l (normal range 0 to 0.25 nmol/l). Other autoantibodies were negative apart from a positive gastric parietal cell antibody. Computed tomography of the mediastinum did not show any thymic abnormality. She was given pyridostigmine 60 mg twice daily, and her symptoms gradually improved. On repeat assessment one month later, there was no evidence of ptosis and the jaw weakness seemed to be improving, though she still needed to hold her jaw when speaking for a few minutes. Repetitive nerve stimulation of left frontalis and obicularis oculi showed no decremental response. Electromyographic examination of the right biceps, extensor digitorum communis, and left frontalis muscles was also normal.
In view of the improving symptoms and the electrophysiological findings, it was decided to continue pyridostigmine alone and steroid treatment was not initiated. Her symptoms continued to improve. By April 2003, she was completely asymptomatic. The pyridostigmine was gradually withdrawn over one month. She remained asymptomatic on follow up in September 2003. Neurological examination was entirely normal although her AchR-abs remained positive at 5.00 nmol/l.
To our knowledge, transient myasthenia gravis has not been described previously in a patient of this age. It is known to occur in 10–15% of infants born to mothers with myasthenia as a result of transplacental transfer of maternal antibodies, and there is a report of transient myasthenia in autoimmune disease resulting from HIV infection.2 In that study, seven HIV infected patients presented with transient myasthenic symptoms. Four of them had positive AchR-abs. In one, myasthenia gravis and coincident autoimmune thrombocytopenia both resolved following anti-retroviral treatment. Our patient had no history of preceding infection, although there was a history of thyroid disease.
The persistence of high levels of AchR-abs despite clinical resolution is of interest. There is no direct correlation between antibody titre and clinical state in individual myasthenic patients.3 The resolution of clinical symptoms and signs, despite persisting acetylcholine receptor antibodies, presumably reflects a positive balance of acetylcholine receptor genesis to antibody mediated destruction.
Late onset myasthenia gravis differs from the typical form in several ways. The HLA DR3 haplotype is uncommon in late onset disease, while thymomas are more common. It is said that late onset disease is more severe and less likely to remit, and that bulbar involvement is more common.4 Response to conventional treatment is also less satisfactory than in younger patients. Our patient was therefore atypical of this older group.
A recent cohort study suggested that myasthenia gravis might be underdiagnosed in older people.5 In that study, 2000 asymptomatic individuals aged 60 and over, who participated in the Oxford healthy aging project, were screened for AchR-abs. Surprisingly, 0.71% were seropositive. Four of eight seropositive subjects had a diagnosis of “stroke” or “transient ischaemic attacks”, and the authors concluded that these patients might have been misdiagnosed.
It is therefore possible that myasthenia gravis in the elderly is sometimes missed and that the clinical course may in some cases be more benign than appreciated.
Competing interests: None declared