The most important clue to myasthenia as a possible diagnosis, is the description of muscle fatigability uncovered during history-taking. The characteristic feature is the fluctuating nature of the motor symptoms, being minimal in the morning and worst in the evening or after exertion. Although most patients with myasthenia may report diurnal fluctuation of their weakness, i.e. feeling best on waking in the morning and experiencing increasing weakness as the day progresses, many neuromuscular specialists have encountered MG patients who complain of ocular symptoms upon awakening that improve during the course of the day [in (Benatar, 2010)]. The examination serves to confirm fatigable weakness which refers to weakening of muscle power with repetitive muscle activity (usually in limbs) or sustained movement (usually with gaze holding). This should be distinguished from a general feeling of fatigue or lethargy (see Table 1).

This chapter will focus on the most common of the myasthenic syndromes which is acquired, autoimmune MG. Apart from specific and comparative clinical details related to the examination findings in the Lambert-Eaton Myasthenic syndromes (LEMS) and the congenital myasthenic syndromes (CMS), the latter two will be comprehensively discussed in their specific chapters.