Myasthenia Gravis in Children
Myasthenia Gravis (MG) is a rare, autoimmune disorder of the neuromuscular junction. In children, it typically presents with fluctuating muscle weakness that worsens with activity and improves with rest. This is a key distinguishing feature from other causes of muscle weakness. The condition is caused by the presence of antibodies against the acetylcholine receptor (AChR) at the neuromuscular junction, which impairs the transmission of nerve signals to the muscle.
Clinical Presentation
The clinical presentation of MG is characterised by fluctuating muscle weakness that is exacerbated by physical activity.
Ocular Symptoms: The earliest and most common symptoms are often related to the small extra-ocular muscles, leading to ptosis (drooping eyelids) and diplopia (double vision).
Generalised Weakness: As the disease progresses, children may develop proximal muscle weakness. This can present as difficulty climbing stairs or getting up from a chair.
Bulbar Symptoms: Symptoms affecting the bulbar muscles (tongue, pharynx, larynx) can lead to dysarthria (slurred speech) and dysphagia (difficulty swallowing).
Myasthenic Crisis: This is a medical emergency and involves severe weakness of the respiratory muscles, which can lead to life-threatening respiratory failure.
Diagnosis
The diagnosis of MG is based on a combination of clinical assessment and specific investigations.
Edrophonium Test: This is a diagnostic test where a short-acting anticholinesterase drug, edrophonium, is administered. A temporary improvement in ptosis and muscle strength is considered a positive result.
Serum Antibodies: The most important diagnostic test is a blood test for anti-acetylcholine receptor (AChR) antibodies. A positive result confirms the diagnosis.
Electromyography (EMG): This can show a characteristic neuromuscular blockade and can help distinguish MG from other neuromuscular disorders.
Management
Management of Myasthenia Gravis is overseen by a specialist paediatric neurologist.
Symptomatic Treatment:
Pyridostigmine: This is a first-line medication that works by inhibiting the enzyme cholinesterase, which breaks down acetylcholine. This increases the amount of acetylcholine available at the neuromuscular junction, improving muscle strength.
Immunosuppression:
Steroids: Oral corticosteroids are often used to suppress the immune system’s attack on the neuromuscular junction.
Other Immunosuppressants: In more severe or refractory cases, other immunosuppressant drugs may be used.
Thymectomy: Surgical removal of the thymus gland (thymectomy) is considered in some cases, particularly in older children and adolescents.
Management of Myasthenic Crisis: This requires admission to a paediatric intensive care unit for close monitoring of respiratory function. Treatment involves intravenous immunoglobulin (IVIG) or plasma exchange to rapidly remove the harmful antibodies from the blood.