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A recent report on three patients who developed myasthenia gravis (MG) three to 10 weeks after cardiac surgery1 raised the intriguing possibility that thoracotomy, by damaging the thymus, could precipitate MG. MG is an autoimmune disorder, associated with autoantibodies that bind to the acetylcholine receptor (AChR) or to muscle specific kinase (MuSK) at the neuromuscular junction. The thymus gland is clearly involved in the aetiology of some cases of MG, probably because the thymic “myoid” cells express acetylcholine receptors.2 In the increasing number of older MG patients,3 however, the cause of the disease is not clear.
Voltage gated potassium channels (VGKCs) are also expressed in the thymus.4 Antibodies to VGKCs have recently been found in some patients with unexplained amnesia,5 and memory loss is common after cardiac surgery, occurring in up to 75% of patients.
For these reasons, we tested sera from 50 persons before and six weeks after cardiac surgery at St Thomas’ Hospital Cardiothoracic Centre. At follow up, they were questioned regarding muscle weakness, visual disturbance or problems with memory, and swallowing difficulties. Five individuals complained of some weakness, and one noted blurred vision. The AChR and MuSK antibodies, however, were negative in all cases. Two men (aged 49 and 57 years) had slightly raised VGKC antibody levels at follow up (107 and 118 pM, respectively, compared with less than 100 pM in healthy controls), but these levels were only slightly higher than the preoperative samples (90 and 106 pM, respectively). Neither complained of muscle weakness or memory problems.
These results do not support the hypothesis that myasthenia gravis or VGKC antibody associated amnesia are frequently precipitated, or the relevant autoantibodies induced, by cardiac surgery. However, since the thymic stroma expresses many self-antigens,6 and is usually damaged during thoracotomy, it would be interesting to assess the prevalence of previous cardiac surgery in patients presenting with these and other late onset autoimmune conditions.
We are grateful to Dr C Scoppetta for sharing the clinical observations that prompted us to perform this study.