Ocular Myotonia

Today, we have heard about several rare diseases and I am about to add another to the pile. This seems to me entirely appropriate to this occasion. Malcolm Campbell, as has been said, was a keen student of natural history. He took a special delight in the recognition of an unusual condition. I should like to add my tribute to his memorial. Myotonia is a sustained contraction of muscle fibres caused by repetitive depolarisation of their membranes (McComas and Johns, 1969). There is good evidence that it is a disturbance of the muscle itself and it can be demonstrated after the neural connections have been blocked. The three disorders in which myotonia occurs are summarised in Table 1. It has been claimed that they are all essentially the same disease but, in general, each type breeds true in any particular family. Myotonia can be demonstrated in three ways. As a failure of relaxation after voluntary contraction it is seen best in the grip of the hand, and, as Thomsen pointed out this makes it difficult for the patient to milk a cow. Myotonia can also be shown by percussion of muscle such as the tongue or thenar group. Needle myotonia is a response to insertion of a needle into the muscle and if a concentric needle electrode is used the electrical discharge can be recorded (figure 6). In dystrophia myotonica there is a combination of myotonia and myopathy. The disability is due mainly to the slow progression of the myopathy. The facial muscles are weak and wasted but not myotonic and clinical tests of eye movement are normal. Ptosis is common and part of the myopathy. The pupil reactions are slow and this has been confirmed by elec-