5.18:
Myasthenia Gravis: Diagnostic Tests
Recall that myasthenia gravis is associated with skeletal muscle weakness and paralysis due to impaired neuromuscular transmission.
The initial diagnosis of myasthenia gravis is generally made based on the symptoms exhibited and the patient's history.
Edrophonium, a short-acting, reversible cholinesterase inhibitor, is used to diagnose myasthenia because of its short-term effects.
The test starts by injecting two milligrams of edrophonium chloride intravenously. If, within forty-five seconds, no effect is observed, an additional eight milligrams is administered.
Improvement in muscle strength lasting about five minutes is a positive indicator of myasthenia.
Myasthenia-associated muscle weakness can be diagnosed using electromyography and repetitive nerve stimulation, which assesses muscle activity in patients.
As anti-receptor antibodies against the nAChRs are prevalent, detecting their presence in plasma or muscle biopsies can confirm the diagnosis.
Because a thymus gland tumor often accompanies myasthenia, imaging tests can help identify any abnormality of the thymus gland.
5.18:
Myasthenia Gravis: Diagnostic Tests
Myasthenia gravis is an autoimmune condition affecting neuromuscular transmission, causing generalized weakness in skeletal muscles. Initial diagnoses rely on patients' signs, symptoms, and medical history. The challenge lies in distinguishing myasthenia from other muscular dystrophies. An important diagnostic feature is the significant improvement of symptoms after administering anticholinesterase inhibitors.
The edrophonium test is a diagnostic tool for myasthenia gravis. It involves administering intermittent intravenous doses of edrophonium chloride, an acetylcholinesterase inhibitor. The test begins with a 2 mg dose, followed by an additional 8 mg dose after 45 seconds if no effects are observed. If there is a noticeable improvement in muscle strength for 5 minutes following the second dose, the diagnosis is considered positive for myasthenia.
Detecting antibodies against nicotinic receptors in plasma samples or muscle biopsies can aid in diagnosing myasthenia gravis. These antibodies disrupt the function of the receptors. Imaging tests, such as magnetic resonance imaging (MRI) or computed tomography (CT), help identify thymus gland tumors, which have a significant role in the pathology of myasthenia gravis. Electrodiagnostic studies, including electromyography and repetitive nerve stimulation, can confirm muscle weakness and assess the impairment of neuromuscular transmission. These tests evaluate nerve conduction and muscle contraction.