Authors
J.B.M. Kuks, M.D., Ph.D.
J.J.G.M. Verschuuren, M.D., Ph.D.
M.H. de Baets, M.D., Ph.D.
Clinical features
The degree of weakness of individual muscles in a given patient may vary considerably. Ocular symptoms Ocular symptoms are most common in MG and part of the patients even have MG restricted to the extra-ocular muscles. Many patients report asymmetric drooping of the eyelids, especially at the end of the day. Double vision or blurring vision disappearing after covering one eye is usual. The double images are mostly on a skew, purely horizontal double vision is rare in MG. Read more
Natural course and prognosis
Because of the use of several drastic therapies the natural course of MG has become uncertain. Before the introduction of immunomodulating therapies a disease related mortality rate of 25-30% was found with most patients dying in the first 5 years of MG; 40% of the patients were reported to improve spontaneously after several years. In most patients the disease gradually develops to a maximum intensity in the first couple of years [6, 11, 24]. Spontaneous long lasting remissions are rare in the first years, but in the long term they may be expected in 10-20% [5, 22, 44, 47, 50]. Patients with ocular MG had a higher remission rate than those with the generalized disease [22, 44]. Read more
Epidemiology
The prevalences of MG are reported around 50-100 x 10 6 [13, 28, 40, 53, 57, 61, 62, 64] with an increased prevalence in more recent studies [47, 61], reflecting both improved diagnosis and a better prognosis in the latter years. MG may become manifest at any age with a peak age at onset in the 20s for females and some 10 years later for males. A second peak is reported between 51-60 years or at higher ages. The bimodal age related incidence peak, the prevalence of thymic abnormalities and HLA phenotypes led to the separation of several patient groups. Read more
Differential diagnosis
Making the diagnosis MG in the patients with MG specific antibodies (a-AChR, anti-MuSK, see below) is not difficult. If no antibodies are found the history, results of clinical examination, reaction to anticholinesterases or findings at electromyography may strongly point to the diagnosis. Nevertheless the diagnosis may remain difficult in a small subgroup of patients. Especially the diagnosis ocular MG may be difficult. Other myasthenic syndromes, especially the Lambert Eaton syndrome always should be considered in seronegative patients with fluctuating weakness. Read more
Ancillary investigations
Several tests may be helpful to confirm the diagnosis MG. Administration of cholinesterase inhibitors (e.g. intramuscular administration of 1.5 mg neostigmin) may lead to a temporary clinical improvement. Read more
Genetics
Although MG is not considered as a hereditary disease with a definite mode of genetic transmission, familial cases have been reported in 1 to 7% of several series [8, 18, 43, 55, 66]. In twin studies, 6 out of 15 monozygotic twins both were affected and none out of 9 dizygotic twins [7].
Familial autoimmune MG seems a rarity but can be confused with congenital MG that is sometimes familial.
In most cases MG occurs sporadically but by taking a careful history it may become clear that other auto-immune diseases as dysthyroidy, insulin dependent diabetes, psoriasis, SLE, rheumatoid arthritis a.o. occur in other members of the family, so an increased chance of developing an autoimmune disease is very likely to be inherited.
