Morning Report: 10/9/2012

MR is back from a small hiatus (vacation!). Here’s Dr. McMillan with today’s edition:

Here’s the case:

You have a 47 year-old male who presents with shortness of breath and leg weakness…

Myasthenia Gravis and Myasthenic Crisis

Myasthenia gravis (Gr mya- muscle; asthenia- paralysis; gravis- grave or serious): A disorder of the neuromuscular junction wherein the body produces antibodies against the motor-endplate acetylcholine receptor (AChR) that results in a “characteristic and striking fluctuating weakness and fatigability of muscle.”

Epidemiology and Pathophysiology

Females affected most from second to third decade, and around 70. Males from fifth to eighth decades. Anti-AChR antibodies cause a reduction in the number and function of AChR at the motor endplate. This in turn results in muscle weakness. Correlation between blood levels of anti-AChR antibodies and severity of disease.

Clinical features

MG patients on therapy can present with myasthenic crisis — inadequate ACh present in the neuromuscular junction, OR in cholinergic crisis, where there is too much ACh in the junction. Diagnosis includes use of assays for anti-AChR antibody level, electromyographic studies, and the edrophonium test. Edrophonium a diagnostic option, but comes with significant risks and not frequently implemented in ER setting.

The most critical complication is respiratory failure. Status best measured with pulmonary function tests:

Table: Pulmonary Function Tests in Patients with Myasthenic Crisis

Adapted from: Mayer SA. Intensive care of the myasthenic patient. NEUROLOGY 1997;48 (Suppl 5): S70-S75.

Acute management

• Supportive: Manage respiratory failure and poor tolerance of oral secretions
• Medical: Cover for any concomitant infection and treat fever, IVIG vs plasmapheresis

Pitfalls

• Not recognizing or addressing threat of impending respiratory failure
• Not recognizing/treating concomitant infection

References:

Mayer SA. Intensive care of the myasthenic patient. NEUROLOGY 1997;48 (Suppl 5): S70-S75.

Ropper AH, Samuels MA. Chapter 53. Myasthenia Gravis and Related Disorders of the Neuromuscular Junction. In: Ropper AH, Samuels MA, eds. Adams and Victor’s Principles of Neurology. 9th ed. New York: McGraw-Hill; 2009. http://www.accessmedicine.com/content.aspx?aID=3642849. Accessed September 16, 2012.

Sloan EP, Handel DA, Gaines SA. Chapter 167. Chronic Neurologic Disorders. In: Tintinalli JE, Kelen GD, Stapczynski JS, eds. Tintinalli’s Emergency Medicine: A Comprehensive Study Guide. 7th ed. New York: McGraw-Hill; 2011. http://www.accessemergencymedicine.com/content.aspx?aID=6366264. Accessed September 16, 2012.

Yavagal DR and Mayer SA. Respiratory Complications of Rapidly Progressive Neuromuscular Syndromes: Guillain-Barré Syndrome and Myasthenia Gravis. Seminars in Respiratory and Critical Care Medicine. Vol 23 (3) 2002, p221-229.

Thanks Dr. McMillan! Leave any comments below.

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Jay Khadpe MD

Editor in Chief of "The Original Kings of County" Assistant Professor of Emergency Medicine Assistant Residency Director SUNY Downstate / Kings County Hospital

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