Myasthenia Gravis In Elderly Man With Slurred Speech

November 8, 2012

The patient had been having slurred speech and trouble swallowing and chewing. He had been using his hand to hold his jaw closed and to push his jaw up to help him chew.

A man in his 70s comes to the emergency department after experiencing 5 days of slurred speech. He is also having some trouble swallowing and chewing, especially at dinner. He reports that he has been using his hand to hold his jaw closed; otherwise it just hangs open. He has also been using his hand to push his jaw up to help him chew.

The patient denies jaw pain, headache, trauma, visual problems, or weakness in his arms or legs. He has had no fevers and he does not use alcohol or illicit drugs. His past medical history is notable for basal cell carcinoma, and hypertension for which he takes furosemide and metoprolol. He is married and denies any recent travel other than to Hawaii where he and his wife own a time-share.

When you enter the examination room, the patient is seated in the position shown.

His vital signs are all within normal limits. Extra-ocular movements are full and without nystagmus. The oropharynx is clear and moist, but phonation seems weak and a bit nasal and speech is slightly slurred. The patient’s teeth and mandible show no tenderness or swelling. His cranial nerves are otherwise intact. Examination of the neck shows no mass, swelling or jugular-venous distention. Examination of the back, chest, and abdomen are all unremarkable and there is no peripheral edema. The neurologic exam is normal except for the findings already mentioned.

Laboratory data, including a complete blood cell count and chemistry panel, are normal except for a potassium level of 3.1 mEq/L (normal, 3.5 to 5.0). CT scans of the brain show only age-related changes.

Based on symptoms of bilateral cranial nerve weakness in an elderly man without other symptoms, myasthenia gravis is at the top of the list of possible causes.

Other causes of symmetric cranial nerve weakness include botulism or use of botulinum toxin for cosmetic concerns and the Miller Fisher variant of Guillain-Barré syndrome. Stroke may cause cranial nerve weakness, but it is unilateral in most cases. A number of systemic conditions can cause symmetric muscle weakness, but they usually affect the limbs initially-especially the legs-rather than the face first. These include hypokalemia, hyperthyroidism, Guillain-Barré syndrome, and Lambert-Eaton syndrome.

Myasthenia gravis usually presents with fluctuating weakness that worsens with prolonged muscle use. It typically starts in the cranial nerves, often causing diplopia, ptosis, trouble chewing or swallowing, and/or a soft/weak voice. With progression, the neck and shoulders may be affected next; eventually other skeletal muscles are involved. Women tend to be affected at a younger age than men.

In contrast with botulism, there should be no anticholinergic symptoms in myasthenia gravis (eg, enlarged pupils or dry mouth and constipation) unless the patient is suffering from a cholinergic crisis from overmedication.

The most feared complication of myasthenia gravis is respiratory failure. Precursors may include shallow respirations, somnolence, and difficulty in handling secretions. When any of these signs are present, measurement of forced vital capacity and arterial blood gases may help determine the need for intubation.

The differential diagnosis includes a short list of neurologic and metabolic conditions (Table). The diagnosis can be confirmed with a Tensilon test (see Table) or with testing for anticholinesterase antibodies.

Treatment depends on the severity of presenting symptoms. Although airway management may be required in a few cases, most patients respond to pyridostigmine alone. Patients with refractory disease may require plasma exchange or IVIG. It is important to look for precipitating symptoms such as infection, pregnancy, or other systemic stressors, as well as new medications (see Table).

Back To Our Patient
A Tensilon test was performed by the ED physician after informed consent was obtained from the patient in this case history. Results were negative, even at the maximum dose. The patient was sent home without therapy because the neurologist was unconvinced that the patient had myasthenia. About 12 days later, however, results of the test for acetylcholine receptor antibodies came back positive, and therapy with pyridostigmine was initiated. This drug led to partial improvement of the patient’s symptoms, but he eventually required plasma exchange before his symptoms were adequately controlled.

See the Table for more details on this condition.

Symptoms:Fluctuating weakness, usually in younger female or older male. Cranial nerve weakness occurs first in 90%, extremity weakness occurs first in 10% Diplopia especially with reading, jaw weakness, dysphagia, soft voice, blurry/double vision
Exam:Pupils normal, ptosis, weakness (especially face, deltoid, neck flexion); may be asymmetric
Red flags:Shallow breathing, tachypnea, PCO
Tests:ABG, chest radiography, TSH, anticholinesterase antibody: positive in 80%
DDx:Hyperthyroidism, hypokalemia, Lambert-Eaton, botulism, Miller Fisher, intracranial mass, stroke
Initial Rx:Stabilize airway, measure FVC, stop corticosteroids and myasthenic meds, determine type of crisis
Cholinergic Crisis:Weakness, miosis, diarrhea/cramps, salivation, sweating,
Rx:Supportive, stop meds
Myasthenic Crisis:Weakness alone caused by: infection, med changes, aspiration, pregnancy, surgery
Rx:Plasma exchange, IVIG, pyridostigmine 60-200 mg PO or 2-6 mg IM BiPAP and/or albuterol may help with oxygenation If intubating, do not use non-depolarizing agents: vecuronium, pancuronium, rocuronium
Avoid:Antibiotics: aminoglycosides, quinolones, tetracyclines, macrolides, chloroquine Cardiac: class 1 antiarrhythmics, local anesthetic, beta-blockers, calcium blockers CNS/Other: phenytoin, corticosteroids, thyroxine, botulinum toxin, vecuronium, pancuronium
Dispo:Admit most. Location may depend on FVC FVC: <20 cc/kg: admit to floor, FVC <15 cc/kg: admit to ICU, FVC <12 cc/kg: intubate

 

Contraindications:Known myasthenia, pregnant
Relative:Asthma, cardiac disease
Side Effects:Bradycardia (treated with atropine),
           Preparation:Consent, cardiac monitor, 10 mg Tensilon in TB syringe, crash cart at bedside
Dosing:Serial progressive doses until positive or 10 mg total: 1 mg, then 3 mg, then 6 mg
Positive test:Improvement within 2 min that lasts <5 min. Start 1 mg; if no effect 3 mg; then 6 mg