Related articles: Myasthenia gravis
Definition
Myasthenia gravis is an autoimmune neuromuscular disease; it involves nerves, muscles and the immune system. At the base of the pathology there is an autoimmune reaction that disturbs the sending of nerve signals from the nerves to the muscles. More specifically, myasthenia gravis is linked to the aberrant production of autoantibodies (autoAc), that is antibodies that, instead of acting against an external agent for defensive purposes, are directed against a part of our body. In myasthenia gravis, the most common type of autoantibody is directed against post-synaptic receptors of the neurotransmitter acetylcholine (AChR). The attack of autoantibodies at the level of the motive plate results in a reduction in the ability of the muscle to contract as a result of the nervous impulse.
The factors that trigger the abnormal immune response are still unknown, however an association with thymic pathologies (eg thymic hyperplasia and thymoma), thyrotoxicosis and other autoimmune disorders has been found.
In myasthenia gravis other types of antibodies can intervene, such as anti-MuSK (anti-tyrosine receptor specific muscle kinase antibodies), while in some patients with generalized myasthenia it is possible not to find autoantibodies in serum ("seronegative" forms). An uncommon form is ocular myasthenia, which affects only the extraocular muscles.
Myasthenia gravis is more common in young women, but can occur at any age.
Most common symptoms and signs *
- Lowering of the voice
- Respiratory acidosis
- Asthenia
- Muscular atrophy
- blepharoptosis
- Language difficulties
- Dysarthria
- Dysphagia
- Dyspnoea
- Muscle pains
- Muscular collation
- Shortness of breath
- Legs tired, heavy legs
- Hypercapnia
- Hypertonia
- weakness
- Muscular hypotrophy
- Leukopenia
- Backache
- Knot in the throat
- Misaligned eyes
- Ophthalmoplegia
- Spastic tetraparesis
- Double vision
- Blurred vision
- Nasal voice
Further indications
Myasthenia gravis is characterized by episodes of muscle weakness (weakness) and fatigability. Muscle weakness worsens with repeated or sustained use of certain muscle groups and decreases with rest, only to reappear on new efforts. The disorder can affect some muscles in isolation, mostly the ocular ones (ocular myasthenia), or all the voluntary muscles in general (generalized form). Frequent symptoms are lowering of the eyelid (ptosis), splitting of the sight and weakening of the muscles of the neck, arms, hands and legs.
Pain is usually not a characteristic symptom of myasthenia gravis, but if the neck muscles are affected, patients may experience back pain due to the effort required to keep the head raised. Some patients have alterations in their voice (often becoming nasal), difficulty in swallowing and a change in facial expressions.
Involvement of the upper chest muscles leads to serious consequences on respiratory mechanics and, in some cases, patients must resort to artificial respiration. Once respiratory disorders have begun, respiratory failure can occur rapidly. The myasthenic crisis, which manifests itself as a severe generalized tetraparesis or a life-threatening weakness of the respiratory muscles, represents a medical emergency that requires hospitalization and immediate treatment.
The diagnosis of myasthenia gravis is formulated on the basis of the serum dosage of antibodies against the acetylcholine receptor (AChR) and of the results of electromyography (EMG) and of the edrophonium test (injected into the muscle, allowing a rapid and transitory improvement of the symptoms and demonstrates the depletion of neuromuscular plaque). Furthermore, considering the known association between myasthenia and thymus pathology it is necessary to complete the investigations with CT and MRI of the thorax.
Treatment of myasthenia gravis includes cholinesterase inhibitors and plasmapheresis to control symptoms. Immunosuppressants, corticosteroids and, in selected cases, thymectomy (surgical removal of the thymus) are used to reduce the severity of the immune system reaction and slow down the course of the disease.
