Myasthenia gravis physical examination
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Fahimeh Shojaei, M.D., Keanu Ngo[2]
Physical Examination
General principles
- Examine for fatigability: test muscles repeatedly against resistance with brief rests, or sustain a posture (upgaze, arms abducted, head lifted supine) for up to 1 minute to provoke progressive weakness.[1]
- Weakness is more proximal than distal, frequently asymmetric in the eyes but often symmetric elsewhere, and is painless with normal sensation, reflexes, and coordination.[2]
- Autonomic function and pupils are spared in autoimmune MG; pupillary involvement suggests an alternative diagnosis such as botulism or third-nerve palsy.[2]
Ocular examination
- Ptosis — typically asymmetric, worsens with sustained upgaze (Simpson test), and may show enhanced ptosis: manually elevating the more ptotic lid worsens ptosis in the contralateral lid, consistent with Hering's law.[3]
- Cogan lid twitch — after sustained downgaze followed by rapid return to primary position, the upper lid overshoots upward and then settles; horizontal-gaze "lid hopping" is a variant.[3]
- Reported sensitivity of the Cogan lid twitch is approximately 75% with specificity approximately 99%; it has demonstrated high interobserver reliability among common eyelid tests for ocular MG.[4][5]
- Ocular motility — fatigable extraocular weakness may range from isolated muscle paresis to complete ophthalmoplegia and can mimic internuclear ophthalmoplegia or a gaze palsy. The cover–uncover test can reveal subtle ocular misalignment.[3]
Orbicularis oculi and facial examination
- Peek sign — with gentle sustained eye closure, the lid margins initially appose and then separate as orbicularis oculi fatigues, exposing sclera. Presence markedly raises the likelihood of MG (LR+ 30.0, 95% CI 3.2–278); absence does not exclude MG.[1]
- Orbicularis oculi weakness — the examiner can separate the lids against attempted forced closure.
- Facial weakness — reduced expression, incomplete lid closure, and a characteristic transverse ("myasthenic") smile; sensation is preserved.[6]
Bulbar and neck examination
- Fatigable dysarthria/dysphonia — speech becomes nasal or slurred with prolonged counting or reading; palatal and tongue weakness may produce nasal regurgitation and dysphagia.[6]
- Neck weakness — flexor weakness is common. Predominant neck extensor weakness ("dropped head") is uncommon and, when present, should raise specific concern for MuSK-antibody disease, which can cause prominent bulbar, facial, and neck weakness with facial/tongue wasting and poor cholinesterase-inhibitor response, or for late-onset AChR disease.[7][6]
Limb and respiratory examination
- Proximal limb weakness — deltoids and hip flexors are commonly affected; demonstrate with sustained arm abduction or repeated sit-to-stand. Finger/wrist extensors and foot dorsiflexors may also be involved.[6]
- Respiratory assessment — in worsening or bulbar disease, assess cough strength, secretion handling, accessory-muscle use, and paradoxical breathing. Respiratory weakness may herald myasthenic crisis.[8]
- Bedside respiratory quantification — when respiratory or bulbar weakness is suspected, supplement inspection with the single-breath count test (counting to approximately 30 in one breath suggests adequate function; ≤20 suggests significant inspiratory muscle weakness), a 3-oz water-swallow observation, and assessment of neck-flexion strength, which correlates with diaphragmatic strength. Paradoxical abdominal breathing is the most reliable clinical sign of impending respiratory failure. Serial vital capacity, negative inspiratory force (NIF), and maximal expiratory pressure (MEP) trends supplement, but do not replace, clinical judgment regarding ventilatory support.[8][9]
Bedside provocative tests
- Ice-pack test — apply ice over a ptotic closed lid for 2–5 minutes; ≥2 mm improvement in ptosis is considered positive. Sensitivity is approximately 85–92% for myasthenic ptosis; specificity is variable across studies (reported 31–98%, and 79–93% in consecutive-cohort series). Summary LR+ is 24.0 and LR− is 0.16. Accuracy may approach that of single-fiber electromyography (SFEMG) of the orbicularis oculi in myasthenic ptosis.[5][6][1][10]
- Anticholinesterase (edrophonium) test — historically used for obvious ptosis or ophthalmoparesis (LR+ 15.0, LR− 0.11), but no longer in routine use after FDA withdrawal of its diagnostic approval in 2018 and because of bradycardia and syncope risk. When a cholinergic challenge is desired, IM neostigmine (1–2 mg) or oral pyridostigmine (30–60 mg) may be used as safer alternatives. False-positive responses occur in motor neuron disease, brainstem lesions, and compressive cranial neuropathies.[6][11]
- Sleep/rest test — reassessment after approximately 30 minutes of sleep or rest is a low-risk alternative; the reported positive sleep-test LR+ is 53.0, although evidence is based on small studies.[1]
Interpretive limitations
- Bedside-test accuracy estimates derive largely from MG-enriched populations and may not generalize to unselected clinic populations; likelihood-ratio confidence intervals can be wide.[1]
- Ice-pack false negatives may occur in mild isolated ptosis, while false positives have been reported in some neuropathies, myopathies, and thyroid eye disease. A positive bedside test therefore does not by itself establish the diagnosis and should be interpreted with serologic and/or electrodiagnostic findings.[10][5]
- A normal pupil examination, sensation, and reflexes supports autoimmune MG, whereas abnormalities in these domains should prompt consideration of alternative diagnoses.[2]
References
- ↑ 1.0 1.1 1.2 1.3 1.4 Scherer K, Bedlack RS, Simel DL (2005). "Does This Patient Have Myasthenia Gravis?". JAMA. 293 (15): 1906–1914. doi:10.1001/jama.293.15.1906.
- ↑ 2.0 2.1 2.2 Gilhus NE (2016). "Myasthenia Gravis". New England Journal of Medicine. 375 (26): 2570–2581. doi:10.1056/NEJMra1602678.
- ↑ 3.0 3.1 3.2 Al-Haidar M, Benatar M, Kaminski HJ (2018). "Ocular Myasthenia". Neurologic Clinics. 36 (2): 241–251. doi:10.1016/j.ncl.2018.01.003.
- ↑ Jienmaneechotchai T, Apinyawasisuk S, Jariyakosol S, Hirunwiwatkul P (2022). "Interobserver and Intra-Observer Reliability of Eyelid Tests for Ocular Myasthenia Gravis". Journal of Neuro-Ophthalmology. 42 (2): 230–233. doi:10.1097/WNO.0000000000001425. PMID 34860746 Check
|pmid=value (help). - ↑ 5.0 5.1 5.2 Claytor B, Li Y (2021). "Challenges in diagnosing coexisting ocular myasthenia gravis and thyroid eye disease". Muscle & Nerve. 63 (5): 631–639. doi:10.1002/mus.27118.
- ↑ 6.0 6.1 6.2 6.3 6.4 6.5 Punga AR, Maddison P, Heckmann JM, Guptill JT, Evoli A (2022). "Epidemiology, Diagnostics, and Biomarkers of Autoimmune Neuromuscular Junction Disorders". The Lancet Neurology. 21 (2): 176–188. doi:10.1016/S1474-4422(21)00297-0. PMID 35065040 Check
|pmid=value (help). - ↑ Morren J, Li Y (2018). "Myasthenia gravis with muscle-specific tyrosine kinase antibodies: A narrative review". Muscle & Nerve. 58 (3): 344–358. doi:10.1002/mus.26107.
- ↑ 8.0 8.1 Claytor B, Cho SM, Li Y (2023). "Myasthenic crisis". Muscle & Nerve. 68 (1): 8–19. doi:10.1002/mus.27832.
- ↑ Elsheikh B, Arnold WD, Gharibshahi S; et al. (2016). "Correlation of single-breath count test and neck flexor muscle strength with spirometry in myasthenia gravis". Muscle & Nerve. 53 (1): 134–136. doi:10.1002/mus.24929.
- ↑ 10.0 10.1 Giannoccaro MP, Paolucci M, Zenesini C; et al. (2020). "Comparison of Ice Pack Test and Single-Fiber EMG Diagnostic Accuracy in Patients Referred for Myasthenic Ptosis". Neurology. 95 (13): e1800–e1806. doi:10.1212/WNL.0000000000010619. PMID 32788239 Check
|pmid=value (help). - ↑ Meriggioli MN, Sanders DB (2009). "Autoimmune Myasthenia Gravis: Emerging Clinical and Biological Heterogeneity". The Lancet Neurology. 8 (5): 475–490. doi:10.1016/S1474-4422(09)70063-8. PMID 19375665.