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Table of Contents    
CASE REPORT
Year : 2021  |  Volume : 69  |  Issue : 2  |  Page : 493-494

An Unusual Case of Muscle Twitching: Its LGI1


Department of Neurology, Sir Ganga Ram Hospital, Old Rajendra Nagar, New Delhi, India

Date of Submission25-Mar-2020
Date of Decision10-Jul-2020
Date of Acceptance14-Jul-2020
Date of Web Publication24-Apr-2021

Correspondence Address:
Dhrumil Jatinbhai Shah
Department of Neurology, Sir Ganga Ram Hospital, Old Rajendra Nagar, New Delhi - 110 060
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0028-3886.314549

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 » Abstract 


A 50-year-old male, presented with a two-months history of ascending paresthesias, with continuous twitchings over the body, associated with insomnia. His electromyography (EMG) revealed neuromyotonia and was diagnosed as a case of peripheral nerve hyperexcitability (PNH) syndrome due to Leucin-rich glioma-inactivated 1 (LGI1) antibody. He showed significant improvement with intravenous immunoglobulin and carbamazepine.


Keywords: Hyperexcitability, LGI1 antibody, neuromyotonia, peripheral nerve
Key Messages: Leucine-rich glioma inactivated 1 (LGI1) antibody is mainly known for characteristic limbic encephalitis. Though rare, it can present with isolated peripheral nerve hyperexcitability (PNH) syndrome showing excellent response to treatment.


How to cite this article:
Tomar LR, Shah DJ, Ranjan R, Rohatgi A, Agrawal C S. An Unusual Case of Muscle Twitching: Its LGI1. Neurol India 2021;69:493-4

How to cite this URL:
Tomar LR, Shah DJ, Ranjan R, Rohatgi A, Agrawal C S. An Unusual Case of Muscle Twitching: Its LGI1. Neurol India [serial online] 2021 [cited 2021 May 14];69:493-4. Available from: https://www.neurologyindia.com/text.asp?2021/69/2/493/314549




Peripheral nerve hyperexcitability (PNH) syndrome is a rare group of disorder.[1] It is characterized by spontaneous and continuous discharges from the peripheral motor nerves. This is commonly an immunological disease and the α-subunit of the voltage gated potassium channel (VGKC) complex {Kv1.1–Kv1.8, Leucine-rich glioma inactivated 1 (LGI1) and contactin-associated protein-like 2 (Caspr2)} is mainly responsible for this syndrome.[2]

LGI1 is associated with the central nervous system involvement and has much lower expression in the peripheral nerve than Caspr2.[2] Although it is known to cause PNH syndrome, isolated LGI1 PNH syndrome is very rare (~7%).[3] They, like Caspr2-associated PNH syndrome, respond well to treatment.


 » Case History Top


A 50-year-old male presented with complaints of paraesthesias that were initially felt in both feet and progressed up to knees in 2 months; he also had continuous twitching movements over arms and thighs but were most prominent over calves [Video 1]. There was no history of sensory loss and weakness or thinning of any limbs. Besides these complaints, he reported having insomnia for last one month. Examination showed continuous undulation of muscle fibers over arms and both the thighs and calf muscles. Cranial nerve examination was normal. There was no muscle atrophy and power at all joints was Medical Research Council grade 5/5. Deep tendon reflexes were all normal with the plantar flexor response and sensory examination was normal.



Electromyography (EMG) of calf muscles revealed doublets, triplets, and multiplets firing at frequency between 150 to 300 Hz suggestive of neuromyotonia [Video 2]. Motor nerve stimulation in lower limbs showed repetitive compound muscle action potentials. Antinuclear antibody was negative and thyroid profile and heavy metal screening were normal. His serum paraneoplastic panel was negative, but the autoimmune panel was tested positive for LGI1 antibody, both in serum and cerebrospinal fluid (done by indirect immunofluorescence). Magnetic resonance imaging of the brain was normal. Whole-body positron emission tomography scan did not reveal an occult malignancy.

So, he was diagnosed as neuromyotonia due to LGI1 antibody and was given carbamazepine (400 mg/day) and intravenous immunoglobulin (2 g/kg for 5 days). He showed dramatic improvement for both paraesthesias and twitching within one week. He was continued on tablet carbamazepine and was completely relieved of his symptoms in 20 days.


 » Discussion Top


Peripheral nerve hyperexcitability syndromes are a heterogeneous group of disorders described by various names (Isaacs' syndrome, Neuromyotonia, Mertens' syndrome, generalized Myokymia), but has a characteristic central feature of “spontaneous and continuous muscle activity.” “PNH syndromes” is the most accepted terminology as the muscle activity is driven by ectopic discharges arising from the distal motor nerve terminals and it is a rare condition.[1]

The VGKC complex is composed of four transmembrane α-subunits and four intracellular β-subunits. Its transmembrane α-subunit determine the VGKC subfamily (include Kv1.1–Kv1.8, LGI1 and Caspr2). The VGKC complex is present in the peripheral, autonomic nervous system and also present in the central nervous system. Blockade of this complex increases nerve excitability leading to repetitive peripheral nerve discharges. It was seen that LGI1 expression in the peripheral nerves was weaker as compared to Caspr-2.[2]

The PNH syndrome manifests with distinctive clinical features like muscle twitching, rippling, stiffness, cramps, and delayed muscle relaxation.[1],[4] Hyperhidrosis, dysesthesias, mild weakness, focal dystonia, and insomnia may be associated.[5] The LGI1 antibody was mainly associated with limbic encephalitis with characteristic faciobrachial dystonic seizures and very rarely involve peripheral nerves as seen in our case.[2],[6] In one large study, only 7% of the LGI1-IgG positive patient had peripheral manifestations alone.[3]

On EMG, the spontaneous activity may range from fasciculations to doublets/triplets/multiplets/myokymia or frank neuromyotonia. They have been described in various neuropathies (inherited/acquired), autoimmune diseases (myasthenia gravis, lupus, and scleroderma), genetic mutations (VGKC), thyroid disease, drugs, toxins, radiation and malignancies (most common: Thymoma, lung cancer).[7] Patients with abnormal EMG findings are more likely to have anti-VGKC antibodies (~40%) than normal EMG findings.[7] In addition, associated autoimmune disorder and autoantibodies has been demonstrated in more than 50% of such cases.[7] Clinically, this patient had none of the above associations.

High dose intravenous methylprednisolone, immunoglobulin and plasmapheresis are beneficial in suspected autoimmune aetiologies.[4],[8] For maintenance, these patients show good symptomatic response to sodium channel blockers like carbamazepine or phenytoin, as they stabilize inactive form of sodium channels.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initial s will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
 » References Top

1.
Isaacs H. A syndrome of continuous muscle-fibre activity. J Neurol Neurosurg Psychiatry 1961;24:319-25.  Back to cited text no. 1
    
2.
Irani SR, Alexander S, Waters P, Kleopa KA, Pettingill P, Zuliani L, et al. Antibodies to Kv1 potassium channel-complex proteins leucine-rich, glioma inactivated 1 protein and contactin-associated protein-2 in limbic encephalitis, Morvan's syndrome and acquired neuromyotonia. Brain 2010;133:2734-48.  Back to cited text no. 2
    
3.
Gadoth A, Pittock SJ, Dubey D, McKeon A, Britton JW, Schmeling JE, et al. Expanded phenotypes and outcomes among 256 LGI1/CASPR2-IgG-positive patients. Ann Neurol 2017;82:79-92.  Back to cited text no. 3
    
4.
Newsom-Davis J, Mills KR. Immunological associations of acquired neuromyotonia (Isaac's syndrome). Brain 1993;116:453-69.  Back to cited text no. 4
    
5.
Irani SR, Vincent A. Voltage-gated potassium channel-complex autoimmunity and associated clinical syndromes. Handb Clin Neurol 2016;133:185-97.  Back to cited text no. 5
    
6.
Liguori R, Vincent A, Clover L, Avoni P, Plazzi G, Cortelli P, et al. Morvan's syndrome: Peripheral and central nervous system and cardiac involvement with antibodies to voltage-gated potassium channels. Brain 2001;124:2417-26.  Back to cited text no. 6
    
7.
Hart IK, Maddison P, Newsom-Davis J, Vincent A, Mills KR. Phenotypic variants of autoimmune peripheral nerve hyperexcitability. Brain 2002;125:1887-95.  Back to cited text no. 7
    
8.
Panagariya A, Kumar H, Mathew V, Sharma B. Neuromyotonia: Clinical profile of twenty cases from Northwest India. Neurol India 2006;54:382-6.  Back to cited text no. 8
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