Myasthenia Gravis Initial Assessment

Clinical Presentation

Patients with MG would present with weakness and fatigability of voluntary muscles. The weakness associated with the disease tends to increase during repeated use and may improve with rest or sleep. Diplopia and ptosis are common initial symptoms and are generally asymmetrical. This may present with Cogan’s lid twitch or excessive lid elevation.

Patients may also present with facial weakness which may result in a snarl-like expression when smiling, accompanied by nasal or slurred speech. Patients may also have trouble swallowing. If the disease is generalized, patients may also experience weakness in the limb muscles that is often asymmetric and proximal. However, deep tendon reflexes and sensations are preserved. In severe cases, there may also be shortness of breath.

MG patients often have associated disorders and should be evaluated as well for these: 

• Thymic abnormalities (eg thymoma, hyperplasia) 
• Autoimmune disorders (eg rheumatoid arthritis [RA], lupus erythematosus [SLE], Grave’s disease, family history of autoimmune disorder, skin disorders) 
• Diseases that may exacerbate MG (eg hyper- or hypothyroidism, infection, medical treatment for other conditions such as antiarrhythmic agents, aminoglycosides, Quinine, etc) 
• Disease states that may interfere with therapy (eg asthma, diabetes mellitus [DM], tuberculosis [TB], peptic ulcer disease [PUD], renal disease, hypertension) 

History

Patients experience weakness and fatigability as described above. The disease can be divided into three stages:

• Active phase: Symptoms typically fluctuate and then become more severe; myasthenic crisis occurs in this phase
• Stable or Inactive phase: Symptoms are stable but still persist; worsening of symptoms are usually attributable to infection, fatigue, tapering of medications, or other identifiable factors
• Burn-out phase: Remission may occur wherein patients are on immunotherapy and symptom-free, or may even be off medications
  • In 15-20 years time, if the symptoms are left untreated, the patient’s weakness becomes fixed wherein the most severely affected muscles become atrophic

The following factors may exacerbate symptoms such as:

• Infection
• Emotional stress
• Thyroid disorder (eg hypothyroidism or hyperthyroidism)
• Hormonal changes particularly menstrual cycle and pregnancy
• Drugs that affect neuromuscular transmission include aminoglycosides, beta-blockers, fluoroquinilones, Penicillamine, Magnesium sulfate, Deferoxamine, macrolides and IV local anesthetics

Physical Examination

On physical examination, the patient may have ptosis and diplopia that improves after rest, sleep (sleep test) or after applying ice on the eyelids (ice test). Repeated testing of muscle strength with periods of rest in between may be done which would show muscle strength that is reduced and worsens with repetition but improves after rest. The following tests may also be done: Quantitative testing of muscle strength (eg motor power survey), forward arm abduction (usually for 5 minutes), and forced vital capacity (FVC). Aside from the weakness, there may be no other neurologic signs.