Laboratory Testing for Myasthenia Gravis

Primary Diagnostic Tests

The American Academy of Ophthalmology recommends anti-acetylcholine receptor (AChR) antibodies as a primary diagnostic test, which can confirm the diagnosis and are present in approximately 80% of patients with generalized myasthenia gravis, though only about 50% of patients with purely ocular myasthenia will test positive 1
Anti-muscle-specific kinase (MuSK) antibodies should be tested when AChR antibodies are negative, as approximately one-third of seronegative patients will be positive for anti-MuSK antibodies 1
Single-fiber electromyography (SFEMG) is considered the gold standard for diagnosis in many centers, with over 90% sensitivity for ocular myasthenia gravis 1, 2
Repetitive nerve stimulation testing is less sensitive than SFEMG, positive in only about one-third of patients with ocular myasthenia 1

The American Academy of Ophthalmology recommends the ice pack test, which may demonstrate reduction of symptoms and is highly specific for myasthenia gravis 1, 3
The Edrophonium (Tensilon) test should be performed by experienced practitioners in a monitored setting with atropine available due to potential muscarinic side effects, and is 95% sensitive for generalized myasthenia and 86% sensitive for ocular myasthenia 1

Pulmonary function assessment, including negative inspiratory force and vital capacity measurements, can evaluate respiratory muscle involvement 4, 5
Creatine phosphokinase (CPK), aldolase, ESR, and CRP tests can evaluate for possible concurrent myositis 4
Cardiac evaluation, including ECG and transthoracic echocardiogram, can rule out concomitant myocarditis if respiratory insufficiency or elevated CPK/troponin T is present 4
MRI of brain and/or spine can rule out CNS involvement or alternative diagnoses, depending on symptoms 4

The American Academy of Ophthalmology recommends avoiding medications that can exacerbate myasthenia symptoms during testing, including β-blockers, IV magnesium, fluoroquinolones, aminoglycosides, and macrolides 4, 5

A CT chest with contrast should be performed after confirming myasthenia gravis diagnosis to evaluate for thymoma, which occurs in 10-20% of patients with AChR-positive myasthenia gravis, and to guide treatment decisions, as thymectomy may be indicated, according to the National Comprehensive Cancer Network 6
CT head without contrast is not indicated as the primary test since the symptoms and electrophysiological findings strongly suggest a neuromuscular junction disorder rather than a central nervous system pathology, as recommended by the American College of Radiology 7