Signs and Symptoms
Symptoms of myasthenia gravis vary from person to person and differences in the age of onset, gender, presence of thymic abnormalities, and the type of self-antibodies present allow the characterization of myasthenia gravis into different subtypes (Meriggioli 2009). The predominant characteristic of myasthenia gravis is easy fatigability, muscular weakness that progressively gets worse with prolonged exercise and is often more pronounced in the evening compared to earlier in the day (Corse 2014; Albertini 2011). Commonly, the first symptom that patients notice is eye muscle weakness, which can affect up to 85% of affected individuals. In 15% of patients, the initial symptom is difficulty swallowing and slurred speech (Meriggioli 2009; NINDS 2012). Disease symptoms usually progress within the first two years, with patients reporting more generalized muscular weakness (Meriggioli 2009). Patients may also have blurred or double vision, drooping eyelids, changes in facial expression and control, difficulty swallowing, and impaired speech (NINDS 2012). As the disease progresses, patients’ arms and legs may also be affected, resulting in difficulty walking. A serious complication of myasthenia gravis called myasthenia crisis may occur in which patients are unable to breathe adequately and may develop respiratory failure requiring mechanical ventilation (Meriggioli 2009).
Patients with muscle-specific tyrosine kinase positive (MuSK+) myasthenia gravis have different symptoms than acetylcholine receptor positive patients. MuSK+ disease primarily affects middle-aged women and muscle weakness is rarely limited to the eye; rather, muscle weakness is also typically found in the face, neck, mouth, and pharynx. Additionally, the thymus is usually normal or very slightly affected in this patient subset. MuSK+ patients are at a higher risk of developing myasthenia crisis and have a lower chance of achieving stable remission (Sieb 2014).
There are several frequently overlooked non-motor symptoms of myasthenia gravis in patients who have thymoma. Pure red cell aplasia (a defect in red blood cell production), weakened immune system, and hair loss are due to CD8+ T cell-induced cell death of white and red blood cell precursors. Spontaneous muscular activity, brain inflammation, heart muscle inflammation, and taste disorders are caused by antibodies to self-proteins. Neurological and cardiac problems are reported in some myasthenia gravis patients with thymoma (Suzuki 2013). Myasthenia gravis can also negatively affect a patient’s quality of life, leading to symptoms of anxiety, depression, and sleeplessness (Basta 2012; Martinez De Lapiscina 2012).
Patients with myasthenia gravis are at an increased risk of developing other autoimmune diseases, including thyroiditis (thyroid inflammation), rheumatoid arthritis, and lupus erythematosus. More recently, clinicians have found a strong association between myasthenia gravis and neuromyelitis optica spectrum disorder (NMOSD) (Sieb 2014). NMOSD causes inflammation of the optic nerves and spinal cord, leading to pain and vision loss, muscle weakness, and occasionally varying degrees of paralysis in the arms and legs (NINDS 2014; Matsumoto 2014). Myasthenia gravis and NMOSD typically occur together in young women. Myasthenia gravis patients also have an increased risk of developing myocarditis (inflammation of the heart) with symptoms including heart failure and arrhythmias (Sieb 2014).