Myasthenia gravis is an autoimmune disease that leads to skeletal muscle weakness and fatigue. The autoantibodies are formed against nicotinic acetylcholine receptors at postsynaptic neuromuscular junction of skeletal muscles. The production of anti-AChR antibodies leads to reduced number of acetylcholine receptors at postsynaptic muscle membrane. This leads to progressive reduction in strength of affected muscles with repeated use. The disease presents with relapses and remissions. Although, it can resolve spontaneously in some patients, for majority of the patients it persists for life. The disease is highly variable and can develop at any age; it is more common in younger women (in their 30s) and men (in their 60s) are affected at older age.
Is There Any Pain With Myasthenia Gravis?
The most common symptom of myasthenia gravis is weakness that is often painless. Weakness can be localized, affecting a particular muscle group or generalized, affecting the whole of skeletal muscles. The hallmark of the disease is the repeated use of muscle lead to increased fatigue. Therefore, the symptoms are worse at the end of the day. The muscle groups that are typically affected are eye muscles, bulbar and proximal skeletal muscles.
The most commonly affected muscles are the eye muscles and affected in more than 75% of the cases. It starts with droopy eyelids and double vision and progresses from mild to severe over weeks to months. In addition, blurry vision and photophobia are commonly reported with exacerbation of ptosis or double vision. Along with extraocular involvement, facial muscle weakness may also ensue that is mostly unilateral. Facial muscle weakness often affects facial expressions giving the impression of tired, sleepy, sad looking face or “myasthenia snarl” when they attempt to smile.
Bulbar symptoms involve the oropharynx leading to problems with chewing, swallowing, speech and respiration. The difficulty chewing or swallowing becomes worse towards the end of the meal. This may even lead to aspiration of food causing higher chances of aspiration pneumonia. Speech becomes slurred due to weakness of the soft palate and the tone of voice becomes nasal. Problems breathing may cause sleep apnea and in minor cases respiratory failure.
Skeletal muscles that are affected are basically the proximal muscles that support in sitting, rising from a chair, walking, climbing stairs, and neck and arm muscles. Patients may complain of weakness of limb muscles with prolonged walking, typing and muscle fatigue with prolonged use. The muscles controlled by autonomic nervous system, such as cardiac, bowel and bladder are not affected by myasthenia gravis.
Although, pain is not a typical feature of myasthenia gravis, patients may complain of pain due to muscle cramps and aches, especially in the neck region. The complaint of pain is not due to myasthenia gravis per se, but secondary to the muscle weakness. Muscle weakness of particular muscles causes extra stress in the surrounding muscles that leads to pain in those muscles. Therefore, pain not being a typical feature of myasthenia gravis is present in these patients subsequent to weakness of muscles and extra stress due to these fatigued muscles that are unable to perform their function to their full capability.
Causes And Risk Factors Of Myasthenia Gravis
Although, the cause of myasthenia gravis is mostly idiopathic, it leads to immune dysfunction with production of IgG antibodies against AChR. Some patients who are negative for anti-AChR antibodies develop antibodies against MuSK (muscle specific kinase).
Various risk factors have been associated with myasthenia gravis that might trigger or exacerbate it. These include, emotional stress, surgery, warm weather, menstruation, immunization, pregnancy and post-parturition, viral infection, worsening of chronic medical conditions (such as autoimmune, renal or cardiac conditions), and certain medications. Medications that can trigger or worsen symptoms myasthenia gravis include, penicillamine, antibiotics (ciprofloxacin, aminoglycosides, ampicillin, clindamycin), beta-adrenergic receptor blocking agents (propranolol), neuromuscular blocking agents (curare, vecuronium), cancer immunotherapeutic agents (ipilimumab), procainamide, phenytoin, lithium, prednisone, verapamil, magnesium, quinidine, chloroquine, timolol, anticholinergics, procainamide, diazepam, ketamine, halothane, phenothiazines and chlorpromazine.