Myasthenia Gravis: Diagnostic Mimics

The clinical hallmark of myasthenia gravis (MG) is fluctuating, painless weakness of muscles that most often affect extraocular, lower bulbar, or limb musculature. Predicting the probability of successful treatment for the patient assumes that the physician has made an accurate diagnosis. In this review, the practical differential diagnosis of MG is reviewed from the perspective of conditions (at presentation of symptoms and signs) that may mimic the disorder. The differential diagnosis includes disorders that limit eye movements (with or without associated diplopia), cause false-positive laboratory studies, and mimic MG but have normal eye movements. The differential diagnosis includes disorders that affect the upper brainstem, cranial nerves, neuromuscular junction, muscles, or local orbit anatomy. Nonneurological systemic diseases (i.e., encephalopathy, sepsis) can produce fluctuating ptosis or eye movements that can occasionally be confused with MG. Although MG is considered often in the differential diagnosis of weakness or fatigue symptoms that lack a correlate on neurological examination (subjective fatigue, breakaway weakness, chronic fatigue syndrome), MG is almost never found.

Myasthenia - diplopia - myopathy - neuromuscular junction - weakness

REFERENCES

• 1 Kaminski H J. Treatment of myasthenia gravis. In: Kaminski HJ Myasthenia Gravis and Related Disorders. Totowa, NJ; Humana Press 2003: 197-222
• 2 Sanders D B. Myasthenia gravis and Lambert-Eaton syndrome. In: Pourmand R Neuromuscular Diseases-Expert Clinicians' Views. Boston; Butterworth-Heinemann 2001: 439-457
• 3 Harper C M. Congenital myopathies and Muscular dystrophies. In: Brown WF, Bolton CF, Aminoff MJ Neuromuscular Function and Disease. New York; WB Saunders Company 2002: 1355-1374
• 4 Mirabella M, Silvestri G, de Rosa G et al.. GCG genetic expansions in Italian patients with oculopharyngeal muscular dystrophy.  Neurology. 2000;  54 608-614
• 5 Meola G, Moxley R T. Myotonic dystrophy and proximal myotonic myopathy. In: Schapira AHV, Griggs RC Muscle Disorders. Boston; Butterworth-Heinemann 1999: 115-135
• 6 Kaukonen J, Zeviani M, Comi G P et al.. A third locus predisposing to multiple deletions of mtDNA in autosomal dominant progressive external ophthalmoplegia.  Am J Hum Genet. 1999;  65 256-261
• 7 Lotz B P. Metabolic myopathies. In: Brown WF, Bolton CF, Aminoff MJ Neuromuscular Function and Disease. New York; WB Saunders Company 2002: 1452-1454
• 8 Cherington M. Clinical spectrum of botulism.  Muscle Nerve. 1998;  21 701-710
• 9 Gutierrez A R, Bodensteiner J, Gutmann L. Electrodiagnosis of infantile botulism.  J Child Neurol. 1994;  9 362-365
• 10 Maselli R A, Bakshi N. AAEM case report 16: botulism.  Muscle Nerve. 2000;  23 1137-1144
• 11 Muley S A, Gomez C M. Congenital myasthenic syndromes. In: Kaminski HJ Myasthenia Gravis and Related Disorders. Totowa, NJ; Humana Press 2003: 309-326
• 12 Glaser J S, Siatkowski R M. Infranuclear disorders of eye movement. In: Glaser JS Neuro-ophthalmology. New York; Lippincott-Williams and Wilkins 1999: 405-460
• 13 Tummala R P, Harrison A, Madison M T, Nussbaum E S. Pseudomyasthenia resulting from a posterior carotid artery wall aneurysm: a novel presentation: case report.  Neurosurgery. 2001;  49 1466-1468
• 14 Moorthy G, Behrens M M, Drachman D B et al.. Ocular pseudomyasthenia or ocular myasthenia “plus”: a warning to clinicians.  Neurology. 1989;  39 1150-1154
• 15 Slamovits T L, Glaser J S. The pupils and accommodation. In: Glaser JS Neuro-ophthalmology. New York; Lippincott-Williams and Wilkins 1999: 542-546
• 16 Thean J H, McNab A A. Blepharoptosis in RGP and PMMA hard contact lens wearers.  Clin Exp Optom. 2004;  87 11-14
• 17 Glaser J S. Orbital disease and neuro-ophthalmology. In: Glaser JS Neuro-ophthalmology. New York; Lippincott-Williams and Wilkins 1999: 489-508
• 18 Leigh R J, Daroff R B, Troost B T. Supranuclear disorders of eye movements. In: Glaser JS Neuro-ophthalmology. New York; Lippincott-Williams and Wilkins 1999: 345-368
• 19 Bromberg M B. Amyotrophic lateral sclerosis. In: Brown WF, Bolton CF, Aminoff MJ Neuromuscular Function and Disease. New York; WB Saunders Company 2002: 1307-1325
• 20 Trontelj J V, Sanders D B, Stalberg E V. Electrophysiologic methods for assessing neuromuscular transmission. In: Brown WF, Bolton CF, Aminoff MJ Neuromuscular Function and Disease. New York; WB Saunders Company 2002: 414-432
• 21 Tawil R, Figlewicz D A, Griggs R C, Weiffenbach B. Fascioscapulohumeral dystrophy: a distinct regional myopathy with a novel molecular pathogenesis.  Ann Neurol. 1998;  43 279-282
• 22 Katirji B. Electrodiagnosis of neuromuscular junction disorders. In: Kaminski HJ Myasthenia Gravis and Related Disorders. Totowa, NJ; Humana Press 2003: 149-175
• 23 Agius M A, Ricman D P, Vincent A. Specific antibodies in the diagnosis and management of autoimmune disorders of neuromuscular transmission and related diseases. In: Kaminski HJ Myasthenia Gravis and Related Disorders. Totowa, NJ; Humana Press 2003: 177-196
• 24 Kuks J BM, Oosterhuis H JGH. Clinical presentation and epidemiology of myasthenia gravis. In: Kaminski HJ Myasthenia Gravis and Related Disorders. Totowa, NJ; Humana Press 2003: 93-113
• 25 Afari N. Chronic fatigue syndrome: a review.  Am J Psychiatry. 2003;  160 221-236