Appendix A: Case Definitions for Neuropsychiatric Syndromes in Systemic Lupus Erythematosus

Myasthenia Gravis

Neuromuscular transmission disorder characterized by fluctuating weakness and fatigability of bulbar and other voluntary muscles without loss of reflexes or impairment of sensation or other neurologic function.

Myasthenia gravis is an autoimmune disorder mediated by antibodies to acetylcholine receptors. It may occur with other diseases of immunologic origin.

Diagnostic criteria:

1. Characteristic signs and symptoms

   One or more of the following:

   1. Diplopia, ptosis, dysarthria, weakness in chewing, difficulty in swallowing, muscle weakness with preserved deep tendon reflexes, and, less commonly, weakness of neck extension and flexion, and weakness of trunk muscles
   2. Increased weakness during exercise and repetitive use with at least partially restored strength after periods of rest
   3. Dramatic improvement in strength following administration of anticholinesterase drug (edrophonium and neostigmine);

and one or more of the following:

2. EMG and repetitive stimulation of a peripheral nerve: In myasthenia gravis repetitive stimulation at a rate of 2 per second shows characteristic decremental response which is reversed by edrophonium or neostigmine. Single fiber studies show increased jitter.
3. Antibodies to Acetylcholine Receptors

Exclusions:

• Congenital myasthenic syndrome, progressive restricted myopathies, steroid and inflammatory myopathies, motor neuron disease
• Multiple sclerosis, variants of Guillain-Barré syndrome (e.g., Miller-Fisher syndrome)
• Organophosphate toxicity, botulism, black widow spider venom
• Eaton-Lambert syndrome
• Stroke
• Medications: neuromuscular blocking agents, aminoglycosides, penicillamine, antimalarial drugs, colistin, streptomycin, polymyxin B, tetracycline
• Hypokalemia; hypophosphatemia

Associations:

• Pure red cell aplasia
• Thyroid abnormalities
• Thymoma

Ascertainment:

• History and physical examination
• Tensilon or neostigmine test (with precautions against respiratory/cardiac complications)
• Anti-acetylcholine receptor antibodies
• 2 Hertz repetitive nerve stimulation (single nerve fiber EMG with jitter studies may be needed)
• Chest CT for thymoma in confirmed myasthenia cases

Record:

• Basic descriptors with the following modification:
• Severity: (Osserman classification) (19):
  I: Ocular myasthenia
  IIA: Mild generalized myasthenia with slow progression: no crises, responsive to drugs
  IIB. : Moderately severe generalized myasthenia : severe skeletal and bulbar involvement but no crises; drug response less than satisfactory
  III: Acute fulminating myasthenia, rapid progression of severe symptoms, with respiratory crises and poor drug response
  IV: Late severe myasthenia, same as III but progression over 2 years from class I to II

(References: 19, 30, 119, 120)

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