alexion test
Diagnosing gMG
Disease onset typically manifests as weakness of the ocular muscles before progressing to more generalised weakness in the majority of patients.1,2 A small subset of patients (about 10–20%) experience symptoms that persistently remain isolated to the ocular muscles (ocular MG).1,2

Despite being a well-characterised autoimmune disease, MG is rare, and at disease onset – which can occur at any age – patients present with highly heterogeneous clinical manifestations (including focal or generalised weakness with varying disease pathophysiology) that often change in nature and severity over time.2,3

Many symptoms of MG may also overlap with a number of other conditions such as thyroid disorders or other muscle diseases.3 Permanent muscle damage rarely occurs in patients with MG,4 so healthcare professionals unfamiliar with the disease may not consider an MG diagnosis for patients whose muscle weakness from the previous day has resolved the next morning.5

Together, these features can make the diagnosis of MG uniquely challenging.6,7

Patients with MG may experience diagnostic delays of several months or even years.7,8

MG is often misdiagnosed in the elderly, as symptoms such as dysphagia, dysarthria or fatigue may be attributed to other causes that can be common in this age group.5,7
Based on the main symptoms a patient may experience, some common differential diagnoses for MG include:3
The diagnostic workup for an individual with suspected MG includes a detailed medical history and physical examination, supported by a number of serological, electrophysiological, imaging and pharmacologic tests.5,9–11
Physical examination may include a detailed evaluation of the patient’s symptoms (ocular, motor, bulbar, respiratory etc.), the quantitative myasthenia gravis test and classification of myasthenia gravis according to the Myasthenia Gravis Foundation of America (MGFA).5,9 A commonly described test for ocular symptoms is the so-called ice pack test, which can help diagnose MG in patients presenting with ptosis. The test involves the application of an ice pack on ptotic eyes for 2–5 minutes to evaluate whether there is improvement of at least 2 mm in ptosis, which would be indicative of MG.4,7,10,12

Anti-AChR autoantibodies

Since the majority of patients with MG (about 80–85%) harbour autoantibodies against the acetylcholine receptor (AChR),1,2,4,10 serum testing for these pathogenic autoantibodies is the first recommended diagnostic investigation when MG is suspected.2,10–12

  • The most widely used method for the detection of anti-AChR antibodies has been the radioimmunoprecipitation assay (RIPA), due to its high specificity (about 99%) and high sensitivity (about 85% in gMG and 50% in ocular MG).2 Modifications of the standard RIPA have been developed to increase the sensitivity compared to the standard RIPA.2
  • Other assays – such as enzyme-linked immunosorbent assays (ELISAs), radiological assays and a fluorescence immunoprecipitation assay (FIPA) – have also been developed, though they tend not to reach the sensitivity of the standard RIPA.2
  • It has been reported that cell-based assays (CBAs) can detect anti-AChR antibodies that are not detectable by RIPA, hence patients who are reported as anti-AChR seronegative with RIPA may be identified as anti-AChR seropositive with CBAs.2 It has also been reported however that CBAs were not able to detect anti-AChR antibodies in patients who were found to have very low but positive titres with standard RIPA.2

Anti-MuSK autoantibodies

In instances where patients are seronegative for anti-AChR antibodies, screening for antibodies against muscle-specific kinase (MuSK) is also recommended; these are present in about 6–8% of patients with MG.2,12
  • RIPA is routinely used to detect anti-MuSK antibodies.2 An alternative method with increased sensitivity includes a step where the samples are concentrated by affinity chromatography before performing the RIPA.2
  • ELISAs are also commercially available for the detection of anti-MuSK antibodies, but are less commonly used.2
  • FIPA seems promising and has been reported to have the same sensitivity as RIPA for anti-MuSK antibody detection.2
  • CBAs have also been developed and were able to detect anti-MuSK antibodies in sera of patients who were identified as seronegative with RIPA.2


Anti-LRP4 autoantibodies

Identification of antibodies against low-density lipoprotein receptor-related protein 4 (LRP4) – a more recently identified diagnostic biomarker of MG – may also have clinical utility in the diagnostic workup of MG in supporting disease subtype classification.10,12,13 At least 2% of patients with MG have detectable anti-LRP4 autoantibodies, though such estimates vary among studies and geographic regions.2,12

  • Several assays have been used to detect anti-LRP4 antibodies, including RIPA, ELISA and CBAs.2
Specialised electrodiagnostic tests are important for diagnosis confirmation in MG, particularly in seronegative individuals as they provide evidence of impaired neuromuscular transmission. These include repetitive nerve stimulation (RNS) and single-fibre electromyography (SF-EMG).12,13 It is recommended that these tests are performed by practitioners experienced in MG diagnoses, with RNS being the initial test and SF-EMG being considered only after receiving a negative RNS test report.11

  • RNS uses a slow rate of repetitive electrical stimulation (2–5 Hz) to examine decline in motor response (the study is positive if the motor response declines by more than 10%).3 In patients with MG crisis, RNS frequency is often abnormal.13
  • SF-EMG assesses the so-called neuromuscular “jitter” during voluntary muscle contraction and is highly sensitive for MG in more than 90% of patients following examination of limb and facial muscles.13
Thymus abnormalities can be central to the pathophysiology of some patients with MG, where up to 15% of patients have tumours of the thymus – or thymomas.12 It is recommended for all patients with suspected MG (ocular or generalised, seronegative or seropositive) to undergo imaging (such as MRI and CT) of the thymus, as well as thyroid function assessment.11 It has also been suggested that all patients with thymoma should be assessed for MG, as up to one-third of thymoma patients develop the disease.12

Pharmacologic tests assessing the clinical response to acetylcholinesterase (AChE) inhibitors are recommended as confirmatory tests for MG diagnoses.11,12
The most known pharmacologic test of this type is the so-called edrophonium test (tensilon test), which involves assessing the patient’s response to intravenous administration of edrophonium chloride – a reversible acetylcholinesterase inhibitor.10,12 The assessment is based on the understanding that disordered neuromuscular transmission in MG is caused by a reduction in the number of functioning AChRs at the postsynaptic membrane.12 Introduction of an AChE inhibitor leaves more available acetylcholine (ACh) to act on its receptors for a longer period, allowing for restoration of muscular function. AChE inhibitors with a immediate-onset and short-lasting activity are preferred.12

In patients seropositive for anti-MuSK antibodies (or patients with suspected MuSK MG), it has been suggested not to perform the edrophonium test, as it may worsen patients’ weakness.12

Expert opinion and local guidelines regarding the use of the edrophonium and other pharmacologic tests – such as neostigmine – differ among countries and should be considered when deciding on the diagnostic workup for MG.12
Several diagnostic algorithms13,14 and local recommendations9,11,15 are available and can be considered when deciding on the diagnostic workup for MG.
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ACh, acetylcholine; AChE, acetylcholinesterase; AChR, acetylcholine receptor; CBA, cell-based assay; CT, computed tomography; ELISA, enzyme-linked immunosorbent assay; FIPA, fluorescence immunoprecipitation assay; gMG, generalised myasthenia gravis; LRP4, low-density lipoprotein receptor-related protein 4; MG, myasthenia gravis; MGFA, Myasthenia Gravis Foundation of America; MRI, magnetic resonance imaging; MuSK, muscle-specific kinase; RIPA, radioimmunoprecipitation assay; RNS, repetitive nerve stimulation; SF-EMG, single-fibre electromyography.
Melzer N, et al. Clinical features, pathogenesis, and treatment of myasthenia gravis: A supplement to the Guidelines of the German Neurological Society. J Neurol. 2016;263(8):1473–1494.
 Lazaridis K, Tzartos SJ. Autoantibody specificities in myasthenia gravis; implications for improved diagnostics and therapeutics. Front Immunol. 2020;11:212. Li Y, Arora Y, Levin K. Myasthenia gravis: Newer therapies offer sustained improvement. Cleve Clin J Med. 2013;80(11):711–721. Gilhus NE, et al. Myasthenia gravis. Nat Rev Dis Primers. 2019;5(1):30.
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