CME INDIA Case Presentation by Dr. V. Arul Selvan, Consultant Neurologist DM (Neuro), MRCP(UK), FRCP (Lond) FRCP (Edin), Royal care super speciality hospital L&T bypass road Coimbatore.

CME INDIA Case Study

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Patient No 1:

Patient No 2:

How Presented?

• Patients presented with twitching of legs, paraesthesia, irritability and insomnia.
• They had hyponatremia and extensive myokymia.
• Most of them had VGKC antibodies positive and some of them had high mercury levels.
• Majority of them had taken native medications in the recent past.

What happened next?

• They were treated with Immuno modulation like IvIg, plasma exchange and Rituximab.
• They all improved well.
• Author had a brief opportunity to work with Ian Hart and Angela Vincent at Oxford who worked extensively in this field.
• One important factor in Indian patients is most of them had been exposed to native medications and high mercury levels.

Significance of this case/Take Aways

• Keep high index of suspicion in patients with twitching of legs, hyponatremia & insomnia and other neuro psychiatric symptoms.
• In such cases do potassium Chanel antibodies.

CME INDIA Discussion

CME INDIA COMMENT by Dr. Ujjawal Roy, DM, Neuro, Ranchi:

CME INDIA Learning Edge

• Myokymia is an atypical and spontaneous form of electrical activity that displays clustered emissions of motor unit action potentials.
• This phenomenon stems from regions of axonal demyelination. The auditory representation of myokymia resembles a rhythmic “marching” pattern.
• The predominant clinical trait of myokymia involves continuous, involuntary undulating motions akin to the movement of worms within muscles.
• This occurrence is most frequently observed in the form of facial or limb myokymia. Facial myokymia may manifest in conditions such as Guillain–Barre syndrome or brainstem impairments, while limb myokymia is evident in cases of radiation-induced plexitis.
• Typically, intervention for myokymia is unnecessary, as it usually lacks symptoms or resolves on its own.

What Happens?

• The origin of these sinuous, wormlike movements emerges from points along the trajectory of motor units, commonly either closer to the extremities or nearer to the origin in the front section of nerve cells known as anterior horn cells.
• In terms of the underlying physiology, unplanned depolarization of axons or anterior horn cells takes place – possibly facilitated through ephaptic transmission – leading to the propagation of an action potential along the diverse motor units to reach the corresponding skeletal muscle fibers.
• Given that each motor unit extends its influence over a multitude of muscle fibers (fewer in the case of facial muscles), the movement of the skin above the contracting muscle cells becomes visibly apparent.

Clinical Presentation

• The recognition of myokymia holds clinical significance, given its association with a limited range of pathological rather than physiological conditions. Additionally, the distinction between generalized and localized myokymia aids in pinpointing its underlying cause.
• A classic example of physiological myokymia is something many of us have encountered: eyelid twitching. However, due to the delicate nature of eyelids, myokymia appears more as a subtle twitch of the eyelid rather than the distinct rippling skin movements commonly seen in facial or limb myokymia.
• Myokymia is observable within both peripheral nervous system and central nervous system disorders.

Clinical myokymia can manifest in various distribution patterns:

1. Focal Myokymia: This localized form primarily affects the facial region, often targeting the chin. It is observed in conditions such as multiple sclerosis, brainstem neoplasms, Bell’s palsy, Guillain–Barre syndrome, or even in individuals with no underlying abnormalities (physiological variations).
2. Limb (Segmental) Myokymia: This type is evident in segments of the body, particularly the limbs. It may be seen in cases of syringomyelia, cervical or lumbar radiculopathies, chronic entrapment neuropathies like median neuropathy at the wrist, and the well-known condition associated with myokymia: postirradiation brachial plexopathy.
3. Generalized Myokymia: This broader presentation is observed in acute inflammatory neuropathies like Guillain–Barre (which, as mentioned earlier, can also present with facial myokymia), or chronic inflammatory neuropathies such as Chronic Inflammatory Demyelinating Polyneuropathy (CIDP). Other conditions contributing to myokymia include uremia, thyrotoxicosis, Isaac’s syndrome, myokymia induced by postexercise, exposure to timber rattlesnake venom, gold therapy, and hereditary episodic ataxia

Basic tests:

• Complete blood count, RFT,LFT,Electrolytes.
• Creatine kinase.
• Thyroid testing group.
• Sedimentation rate.
• Lyme titer.
• Venereal Disease Research Laboratory (VDRL) test.
• Rheumatology screening.
• Serum alcohol level and toxic screen are recommended for acute onset of generalized myokymia.

Antibodies targeting Voltage-Gated Potassium Channels (VGKCs)

• These have links to neuromuscular weakness, notably seen in conditions like neuromyotonia (also referred to as Isaac’s syndrome) and Morvan syndrome.
• These VGKC antibodies are also connected with paraneoplastic neurological syndromes and limbic encephalitis.
• However, in cases of VGKC antibody-associated limbic encephalitis, the presence of antibodies to leucine-rich, glioma-inactivated 1 protein (LGI1) or contactin-associated protein-2 (CASPR2) is more common, as opposed to antibodies targeting potassium channel antigens. It’s worth noting that a significant portion of VGKC antibody-positive instances do not exhibit LGI1 or CASPR2 IgG autoantibodies, and not all VGKC complex antigens are fully understood.
• The clinical relevance of this testing can only be fully grasped when considered alongside the patient’s clinical history and other relevant laboratory evaluations

Morvan syndrome

• Clinical Presentation: Morvan syndrome presents with a combination of diverse clinical features, which can make diagnosis challenging. These features may include myokymia, neuropsychiatric symptoms, autonomic dysfunction, and insomnia.
• Diagnostic Investigations: Standard investigations like cerebrospinal fluid (CSF) analysis, brain MRI, electroencephalography (EEG), and positron emission tomography (PET) scans might not provide definitive diagnostic results in Morvan syndrome cases.
• Electromyography (EMG): EMG studies can help confirm the presence of myokymia, a characteristic muscle movement seen in Morvan syndrome.
• VGKC-Complex Antibodies: Detection of voltage-gated potassium channel (VGKC)-complex antibodies, especially those directed against CASPR2 and LGI1, can be highly diagnostic for Morvan syndrome. CASPR2 antibody predominance is often associated with cases involving thymoma.

CME INDIA Tail Piece

• Over a century ago, the term “myokymia” was initially employed by Schultze to depict persistent, gradual, and wave-like contractions of the small muscles within the hands and feet. In a related context, Kny introduced the phrase “myoclonus fibrillaris multiplex” to characterize comparable clinical presentations.

References:

1. Misawa T, Mizusawa H. [Anti-VGKC antibody-associated limbic encephalitis/Morvan syndrome]. Brain Nerve. 2010 Apr;62(4):339-45. Japanese. PMID: 20420173.
2. Irani SR, Pettingill P, Kleopa KA, Schiza N, Waters P, Mazia C, Zuliani L, Watanabe O, Lang B, Buckley C, Vincent A. Morvan syndrome: clinical and serological observations in 29 cases. Ann Neurol. 2012 Aug;72(2):241-55. 
3. Suresh Kumar PN, Sajithlal E, Shamsudeen M, Kumar RP. Morvan’s syndrome Presenting with Psychiatric Manifestations – A Case Report and Review of the Literature. Neurol India. 2022 May-Jun;70(3):1207-1209. doi: 10.4103/0028-3886.349616. PMID: 35864667.
4. Rueff L, Graber JJ, Bernbaum M, Kuzniecky RI. Voltage-gated potassium channel antibody-mediated syndromes: A spectrum of clinical manifestations. Rev Neurol Dis 2008;5:65-72

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