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A thorough examination of patients’ symptoms is necessary to diagnose Myasthenia Gravis. Keeping a record of the weaknesses and the fatigue of the more involved muscle groups at various times is important. In cases where only one muscle group is affected, this is most likely the eye muscles (ocular myasthenia), this diagnosis is even more complicated.

 

The next step is the clinical examination, which involves provocation of the weaknesses in each muscle group by exercise tests. This clinical examination should be done if it is already obvious that Myasthenia Gravis is suspected or to rule out any doubts about the diagnosis ie some other neurological disorder must be eliminated.

 

Here are the following tests to confirm or eliminate Myasthenia Gravis:

 

Electrtrophysiology examination - repetitive stimulation involves using an electrical stimulus where an electrode needle is applied to the skin overlying the nerve, the nerve then activates and sends the signal to the muscle supplied by that nerve. The above procedure is repeated (application of the repetitive stimulus). If there is a decline of the action potential in the first four to five muscle responses of more than 10%, this means it is a disorder in neuromuscular transmission.

Single Fibre EMG (SFEMG) is a more sensitive test of neuromuscular transmission where a small needle is inserted within a single muscle fibre. Extension or blocking of the action can mean a disorder but can be also seen in other neuromuscular diseases.

Medication tests can be helpful mainly in case of the ocular form of the disease. After the short effected inhibitor of cholinosterase (neostigmin - Tensilon is not available in the Czech Republic) is injected, we monitor if there is any improvement of the weakness in the eye muscles (see the youtube video). Sometimes an ice test can be performed where the dropped eyelid is improved after it has been covered with an ice pack.

 

The detection of antibodies to the acetylcholine receptor (AChR) is detectable in about 80% of patients. The detection is done by routine blood test. In cases when the results are normal and the diagnosis is probable, the examination of antibodies to protein called muscle specific tyrosine kinase (MuSK) is performed. This protein, as well as AChR, are situated on postsynaptic membrane and are necessary for transforming AChR into the membrane. These antibodies are positive in about 40% of patients with negative AChR. T  In some patients there is a  presence of thymoma and some older patients have positive antibodies against antistriatal antibodies (ASMaB). These antibodies are routinely not examined.

 

Computed tomography (CT scan) of the breastbone where the contrast material is placed may identify the presence of thymoma (approximately 10-15% of patients with Myasthenia Gravis). In most cases there is an absence of malignant tumor, but sometimes abnormal cells can be spread into fibrous tissue and local radiation after the surgery is given. However, even if the thymoma is removed by surgery, it does not mean that Myasthenia Gravis is cured. Patients must take the medication that inhibits pathological immune reaction permanently. In some cases, the thymoma without any symptoms of Myasthenia Gravis can be found, most likely randomly, and Myasthenia Gravis can appear even many years after the removal.

 

Thank you for the translation Sonya