Anti-CASPR2-Antibody-Positive Isaacs' Syndrome Presenting with Myokymia, Neuropathic Pain, and Hyperhidrosis

Anti-contact protein-associated protein 2 antibody encephalitis in children: A case report

BACKGROUND

Anti-contactin-associated protein-like 2 (CASPR2) antibody encephalitis is an autoimmune disorder characterized by the presence of antibodies against the voltage-gated potassium channel. This leads to neurological symptoms, such as seizures, cognitive decline, and neuropathic pain, primarily affecting the limbic system. The prognosis of this disorder varies among individuals.

CASE SUMMARY

The patient, a girl aged nine years and nine months, underwent treatment for 14 to 21 d. The main clinical manifestations were vomiting and unclear consciousness, positive pathological signs, normal cranial computed tomography and magnetic resonance imaging, and abnormal electroencephalogram. The child was discharged after receiving immunoglobulin and hormone treatment. Subsequent follow-up over a period of 15 months after discharge, conducted through telephone and outpatient visits, showed no recurrence of symptoms.

CONCLUSION

Anti-CASPR2 antibody autoimmune encephalitis in children is rare, mainly manifested as convulsions, mental abnormalities, cognitive impairment, and neuropathic pain, among others. Timely evaluation for autoimmune encephalitis antibodies is crucial, especially in cases of recurrent central nervous system involvement in children.

Systematic Review of the Clinical Characteristics and Management of Isaac Syndrome

OBJECTIVES

Isaac syndrome (IS) is a condition characterized by peripheral nerve hyperexcitability caused by voltage-gated potassium channel (VGKC)-complex antibodies. Muscle twitching, stiffness, hypertrophy, and dysautonomic characteristics, such as hyperhidrosis, are common manifestations. The syndrome can be autoimmune or paraneoplastic, with thymoma being a common cause of paraneoplastic IS. Furthermore, this condition could be handed down from one generation to another. However, there is limited information regarding outcomes, relapses, associated syndromes, associated malignancies (other than thymoma), and treatment options. Despite its rarity, there remains a need for effective management strategies for patients with IS. To address this gap, we conducted a systematic review to summarize the most common and effective treatments of IS in immunomodulatory agents and symptomatic medications, as well as to describe outcomes, relapses, and associated malignancies. Altogether, this review serves to guide clinical practice recommendations for IS and highlight areas for further research.

METHODS

We used the Preferred Reporting Items for Systematic Reviews and Meta-Analyses protocol to conduct a systematic review of cases reposted through the PubMed and Google Scholar databases. The terms "Isaac Syndrome" and "Acquired Neuromyotonia" were used. The Joanna Briggs Institute's critical appraisal tool was used to evaluate the quality of the included studies.

RESULTS

We identified 61 case reports and 4 case series, comprising a total of 70 patients with IS (mean age at onset: 42.5 ± 18 years, and 69% were males). Fourteen cases reported relapses. Thymoma was the most common malignancy associated with IS, followed by lymphoma. Among various serum antibodies, voltage-gated potassium channel-complex antibodies were the most reported antibodies elevated in IS (reported in 38 patients and elevated in 21 patients [55.2%]), followed by acetylcholine ganglionic receptor antibodies, which were reported in 30% of patients (n = 21) and were elevated in 5 cases. The most common electromyography findings were myokymic discharges (n = 22), followed by fasciculations (n = 21) and neuromyotonia (n = 19). For treatment, combining anticonvulsants such as carbamazepine with immunotherapy therapy showed the best results in controlling the symptoms. Among immunotherapy therapies, the combination of plasma exchange plus intravenous high-dose steroids achieved the best results in the acute treatment of IS ([n = 6], with improvement noted in 83.3% [n = 5] of cases). Among the symptomatic treatments with anticonvulsants, carbamazepine was the most efficacious anticonvulsant in treatment of IS, with an average effective dosing of 480 mg/day (carbamazepine was used in 32.3% of acute treatment strategies [n = 23], with improvement noted in 73.9% [n = 17] of cases).

CONCLUSIONS

IS a rare neuromuscular syndrome that tends to affect middle-aged men. These patients should be screened for thymoma and other malignancies such as lymphomas. The management of IS symptoms can be challenging, but based on our review, the combination of multiple immunosuppressives such as IV steroids and plasmapheresis with anticonvulsants such as carbamazepine seems to achieve the best results.

A Rare Phenomenon of Isaacs Syndrome: A Case Report

We illustrate the case of a 71-year-old male who initially presented with sudden onset muscle weakness and ambulation difficulty. Following medication discontinuation and additional clinical studies, he failed to improve and was admitted to the hospital 11 weeks later. He had an associated 20-pound weight loss, sudorrhea, and muscle stiffness only when weight-bearing. A complete connective tissue cascade and a paraneoplastic panel were obtained. Clinical diagnosis of acquired neuromyotonia, or Isaacs syndrome (IS), was made, and he began experiencing significant improvement after intravenous steroid infusion. IS is a rare disease that has been poorly documented in the literature. There have only been a limited number of cases which are globally documented. One of the difficulties is a lack of definite autoantibody with which to correlate the disease; however, there has been some correlation linking the disease to voltage-gated potassium channels. Ultimately, the diagnosis should be driven by history and clinical presentation. The aim of this case report is to highlight a rare disease process and increase awareness among clinicians. We also describe the associated evaluation and recommended treatment for an optimal patient outcome.

Autoimmune neuromyotonia

PURPOSE OF REVIEW

Autoimmune neuromyotonia encompasses a group of rare immune-mediated neurological disorders frequently associated with anti-contactin-associated protein-like 2 (CASPR2) antibodies and featuring clinical and electrical signs of peripheral nerve hyperexcitability (PNH). We aim to summarize the current knowledge on immune-mediated neuromyotonia, focusing on clinical presentations, pathophysiology, and management.

RECENT FINDINGS

Neuromyotonia is a major feature of several autoimmune neurological syndromes characterized by PNH with or without central neurological system involvement. Experimental and clinical evidence suggest that anti-CASPR2 antibodies are directly pathogenic in autoimmune neuromyotonia patients.

SUMMARY

Neuromyotonia, a form of PNH, is a major feature in several syndromes associated with anti-CASPR2 antibodies, including cramp-fasciculation syndrome, Isaacs syndrome, Morvan syndrome, and autoimmune limbic encephalitis. Diagnosis relies on the identification of motor, sensory, and autonomic signs of PNH along with other neurological symptoms, anti-CASPR2 antibody-positivity, and of characteristic electroneuromyographic abnormalities. Paraneoplastic associations with thymoma are possible, especially in Morvan syndrome. Patients usually respond to immune-active treatments, including steroids, intravenous immunoglobulins, plasma exchanges, and rituximab.

Neuromuscular hyperexcitability syndromes

PURPOSE OF REVIEW

To provide an update on recent developments regarding acquired, antibody-mediated, neuromuscular hyperexcitability syndromes, including Isaac's and Morvan's syndromes, cramp-fasciculation syndrome and rippling muscle disease, and their genetic differential diagnoses.

RECENT FINDINGS

Antibodies in auto-immune peripheral nerve hyperexcitability syndromes (PNHS) are directed against CASPR2 and LGI1, proteins of the voltage-gated potassium channel (VGKC) complex. We discuss the significance of 'double-negative' VGKC antibodies in PNHS and the rationale for ceasing VGKC antibody testing (but testing CASPR2 and LGI1 antibodies instead) in clinical practice. Recent case reports also expand the possible clinical phenotypes related to CASPR2/LGI1 antibodies, but the interpretation of these findings is complicated by the frequent association of antibody-mediated neuromuscular hyperexcitability syndromes with other auto-immune disorders (e.g. myasthenia gravis).Finally, a hereditary origin of neuromuscular hyperexcitability should always be considered, even in non-VGKC-related genes, as evidenced by the recently discovered high frequency of HINT1 mutations in people of Slavic origin.

SUMMARY

This review provides an update on recent clinical, immunological and genetic developments in neuromuscular hyperexcitability syndromes. We also provide a guide for the clinician for diagnosing and managing these disorders in clinical practice, with a special focus on the main differential diagnoses.