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Myasthenia Gravis F041

Last amended 
2 July 2015
Current RMA Instruments
Reasonable Hypothesis 75 of 2015
Balance of Probabilities 76 of 2015
Changes from Previous Instruments

SOP Bulletin 184

ICD Coding

  • ICD-10-AM Codes: G70.0
  • ICD-9-CM Codes: 358.0
Brief description:

This is a neurological disorder affecting any part of the nervous system that has skeletal neuromuscular junctions. The disorder is an autoimmune disorder which affects the transmission of impulses from the nerve to muscle causing muscle fatigue and weakness. The skeletal muscles involved are in the eye (ocular), cranial nerves of brain stem (bulbar), limbs, or respiratory muscles. As such myasthenia gravis is also subdivided into ocular myasthenia and generalised myasthenia types.

Confirming the diagnosis:

To confirm the diagnosis there needs to an opinion from a specialist neurologist.

The neurologist will utilise the following types of diagnostic tests:

  • MRI and CT brain and spinal cord imaging to exclude other diseases.
  • Repetitive nerve stimulation
  • Electromyography
  • Serum antibodies to anticholinesterase receptors
  • Serum antibodies to muscle specific tyrosine kinase
  • Challenge testing with edrophonium
  • Challenge testing with ice packs

The majority of cases will have autoantibodies to the acetylcholine receptor in the neuromuscular junction or antibodies to muscle specific tyrosine kinase.  A small subset (6-12%) will not, but are still covered by the SOP.

The relevant medical specialist is a neurologist and if the eye is involved ophthalmologist.

Additional diagnoses covered by these SOPs
  • Ocular myasthenia
  • Generalised myasthenia
  • Seropositive myasthenia gravis
  • Seronegative myasthenia gravis
Conditions not covered by these SOPs
  • Temporary myasthenia due to medication#
  • Myasthenia syndromes not being myasthenia gravis#                        

* another SOP applies  - the SOP has the same name unless otherwise specified

# non-SOP condition

Clinical onset

The clinical onset will be the earliest time when both the necessary myasthenia symptoms and signs were present prior to the formal diagnosis of myasthenia gravis. Note that the clinical onset can be complicated if it was associated with a drug which also causes temporary myasthenia. Note that this SOP specifically excludes ‘…temporary weakness and fatigability of skeletal muscles due to medication…’. Hence there may be situations where the myasthenia gravis was effectively asymptomatic and was incidentally diagnosed when the use of a medication caused temporary weakness and fatigability of skeletal muscles prompting the medical investigation of myasthenia gravis. Under this circumstance the myasthenia gravis did not as yet have a clinical onset at the time of the use of the medication which provoked the medical investigation and the diagnosis of the occult myasthenia gravis.  There are however circumstances where the myasthenia gravis was weakly symptomatic (did have a clinical onset), and the use of a medication causing temporary weakness and fatigability of skeletal muscles provided the early diagnosis of the myasthenia gravis.

Clinical worsening

The condition has to have had a clinical onset before a clinical worsening can be considered. This is a complicated disease, which would require a specialist neurologist opinion to assess whether any evident clinical worsening was out of keeping with the natural progression of the underlying pathology in this client.

Comments on SOP factors

As noted above the ‘having systemic treatment with a drug from the specified list at the time of the clinical onset’ depends on whether the myasthenia gravis was really active (was in clinical onset) at the time of the systemic drug treatment, or whether the clinical presentation was solely the result of the systemic drug treatment with no material contribution from the myasthenia gravis.