MYASTHENIA GRAVIS   60A

A 35-year-old woman presents to the clinic complaining of double vision (diplopia) intermittently with progressive worsening over 2 months. In addition, she has noted intermittent drooping of her eyelids (ptosis). She works as a computer programmer, and both the diplopia and ptosis seem to worsen with prolonged computer work. Both symptoms subside with rest. She is generally fatigued but has no other weakness or neurologic symptoms. Her medical history is unremarkable. Physical examination is notable only for impaired lateral movement of the right eye and bilateral ptosis, both of which worsen with repetitive eye movements. Motor, sensory, and reflex examinations are otherwise unremarkable.

What are the salient features of this patient’s problems? How do you think through her problems?

Salient features: Young woman with diplopia and ptosis; intermittent but progressive symptoms; bilateral eye muscle weakness, which worsens with repetitive eye movements and improves with rest

How to think through: Diplopia should always be carefully evaluated. Although it has many possible etiologies, what serious causes should be considered on initial evaluation? (Intracranial structural lesion or bleeding, temporal arteritis, thyroid ophthalmopathy, botulism, and others.) What is the pattern of symptoms seen in myasthenia gravis (MG)? (Daily fatigability, fluctuation of severity over weeks.) In addition to young women, what other demographic group is most often diagnosed with MG? (Older men.) What other comorbid and familial diseases occur with MG? (Autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus, Hashimoto thyroiditis, and Graves disease.) What muscle groups should be examined? (Ocular, bulbar [dysphagia, dysarthria], respiratory, and limb muscles.) Does MG affect the pupils? (No. This can help distinguish MG from botulism and third cranial nerve compression.) Does MG affect the sensory system? (No.) What causes muscle weakness in MG? (Autoantibodies to acetylcholine receptors or to muscle-specific receptor tyrosine kinase [MuSK].) How can we confirm the diagnosis? (Acetylcholine receptor antibody testing; electrophysiologic testing, including repetitive nerve stimulation and electromyography.) When MG is diagnosed, it is important to evaluate the thymus gland for thymic hyperplasia (present in 85% of patients with MG) and thymoma (in 15%). Thymoma resection can improve MG symptoms. What is the mainstay of MG treatment? (Anticholinesterase drugs.)

MYASTHENIA GRAVIS   60B

What are the essentials of diagnosis and general considerations regarding myasthenia gravis?

Essentials of Diagnosis

Fluctuating weakness of voluntary muscles, producing symptoms such as diplopia, ptosis, and difficulty in swallowing

Activity increases weakness of affected muscles

Short-acting anticholinesterases transiently improve the weakness

General Considerations

MG is most common in young women with HLA-DR3 and in older men with associated thymoma.

MG is also associated with thyrotoxicosis, rheumatoid arthritis, or systemic lupus erythematosus.

The onset is usually insidious but may be unmasked by a coincidental infection.

Exacerbations may occur before the menstrual period and during or shortly after pregnancy.

Symptoms are attributable to blockage of neuromuscular transmission caused by autoantibodies binding to acetylcholine receptors.

The external ocular muscles and certain other cranial muscles, including the masticatory, facial, and pharyngeal muscles, are especially likely to be affected.

The respiratory and limb muscles may also be involved.

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