Treatment for Myokymia
The treatment for myokymia depends on its underlying cause, with carbamazepine being the most effective first-line medication for idiopathic cases, showing benefit in 83% of patients with superior oblique myokymia. 1
Types and Causes of Myokymia
- Myokymia is characterized by undulatory muscle spasms resembling a worm's crawl, which can affect various muscle groups 2
- It can be classified into two main types: facial myokymia and limb myokymia 2
- Myokymia can be caused by various conditions including multiple sclerosis, hypothyroidism, Guillain-Barré syndrome, radiation plexopathy, pontine tumors, and timber rattlesnake envenomation 3
- What appears as benign eyelid myokymia may sometimes progress to facial myokymia, potentially indicating underlying brainstem disease such as multiple sclerosis 4
Diagnostic Approach
- Electromyography (EMG) is crucial for diagnosis, showing spontaneous continuous motor unit activity and/or electrical myokymia with grouped discharges at an interburst frequency of 2-300 Hz 5
- For ocular myokymia, the ice test (applying an ice pack over closed eyes for 2 minutes) can be helpful in differentiating it from myasthenia gravis 6
- When myokymia is associated with neurological symptoms, imaging may be necessary to rule out underlying conditions like multiple sclerosis 4
Treatment Options
First-line Treatments
- Carbamazepine is the most effective first-line treatment for idiopathic myokymia, with 83% of patients showing some benefit 1
- For superior oblique myokymia specifically, carbamazepine provides sustained benefit in many patients 1
Alternative Medications
- Phenytoin can be effective in cases that don't respond to carbamazepine 5, 1
- Propranolol alone or in combination with valproic acid has shown benefit in some patients with superior oblique myokymia 1
- Baclofen has not shown treatment success for superior oblique myokymia 1
Treatment for Underlying Conditions
- When myokymia is secondary to another condition, treatment should target the underlying cause 2
- For myokymia associated with myasthenia gravis, pyridostigmine bromide (60mg orally 2-4 times daily) is the first-line treatment 7
- In myasthenia gravis with inadequate response to pyridostigmine, corticosteroids should be added 7
- Immunosuppressive therapy with azathioprine can be considered for patients with moderate to severe disease when myokymia is related to autoimmune conditions 6
Monitoring and Follow-up
- Long-term follow-up is important as some patients may experience only transient improvement with medication 1
- Approximately 45% of patients with superior oblique myokymia enjoy sustained benefit from medical treatment without adverse side effects 1
- For myokymia that progresses to involve multiple facial muscles, further neurological evaluation is warranted 4
Pitfalls and Considerations
- What initially appears as benign eyelid myokymia may sometimes be the first manifestation of a more serious neurological condition 4
- The biochemical mechanism of myokymia may involve decreased ionized calcium in the microenvironment of the axon, affecting membrane excitability 3
- Some medications should be avoided in patients with myasthenia gravis-related myokymia, including β-blockers, IV magnesium, fluoroquinolones, aminoglycosides, and macrolides 6