Case Study: Myasthenia Gravis

Question 1

Demonstrate, list, or recognize discriminating components of the clinical history of a patient presenting with fatigue, including bio-psycho-social element

Answer 1

MA is specific muscle weakness/fatigue (w/ use of exerstion and force)!!! not generalized…

Generalized includes symptoms of stress and depression (both of these cause everything), drinking, stroke, etc

Question 2

Describe the following for myasthenia gravis:

• Pathophysiology
• Typical presentation
• Evaluation
• Natural history and progression

Answer 2

Pathophysiology: muscle weakness with repetitive useage; autoantibodies against AChR impairing NMJ mechanism; 75% have thymic diease- T_H2 cells involved with stimulating proliferation of antibodies

Typical presentation:

• 50-85% have ocular symptoms w/ generalized weakness
• 20% with bulbar symptoms (problems with phonation, the formation of speech sounds involving breath, vocal cords, tongue, palate and other structures)
• Weakness of head flexion and extension
• Proximal limb weakness
• Symptoms might fluctuate but will be progressive!!

Evaluation:

• Ice cube test: cold improves neuromuscular transmission in MG by decreasing the rate of breakdown of ACh
• Edrophonium test: bedside test using a measured IV dose of this very short acting anticholinesterase –> prevents breakdown of ACh and therefore, increases the ACh available at the neuromuscular junction. The patient with diplopia or ptosis due to MG will have an improvement, albeit brief, in their symptoms.
• Medical Imaging of Thymus
• AChR antibodies are a specific test for MG, though a small percentage of patients do not have these antibodies.
• RNS and SFEMG support a diagnosis of MG

Natural history and progression

Question 3

Describe appropriate management for a patient with myasthenia gravis

Answer 3

Because treatment has been empirical for a long time, treatment practices and preferences are influenced by convention and opinion and experience.

Immunosuppressants, thymectomy, IV immunoglobins, and plasmapheresis best medications!

versus

Cholinesterase inhibitor can cause cholinergic crisis! Corticosteroids have many adverse effects, and though they help this autoimmune disease, they are not the best medication for long term management.

Question 4

Both conditions may present with weakness and respiratory dysfunction. How would you tell the difference? Differentiate between myasthenic crisis (exacerbation of MG crisis) and cholinergic crisis in an clinical vignette.

(Hint: Patients on medication may experience cholinergic crisis due to overdose of cholinesterase inhibitor medication.)

Answer 4

Excessive Acetylcholine effect characteristic of cholinergic crisis is associated with excess parasympathetic symptoms (“rest and digest”), which you can see in the comparison lists above. Remember that miosis is constricted small pupils. Fasciculation is “twitching” of the affected muscles.

Cholinergic Crisis has PNS symptoms!!!

Question 5

Describe medico-legal, ethical and psychosocial issues potentially affecting patients with myasthenia gravis

Answer 5

Medico-legal: errors in medical practice (missed diagnosis, failure to monitor antibodies of fetus, hypoxia injuries due to failure to recognize/monitor/assess respiratory failure)

Ethical: morals (termination of pregnancy, decision-making)

Psychosocial: loss of/challenges to patient’s independence (driving, power-of-attorney, depression/anxiety, insurance, employment, driving, parenting/pregnancy)

Question 6

Myasthenia Gravis - Epidemiology

Explain how incidence is stable but prevalence has increased.

Answer 6

_*Classic Step 1 Question*_

We once thought that MG was much more prevalent in women than men. However, as the average life span of men increases, it has been noted that men develop the disease, too, but are affected at older ages.

Age of onset higher in men (>50 years vs. 20-30 in females) –> since men are living longer there is an increase in prevalence.