Short communication
Reduplicative paramnesia in Morvan's syndrome

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Abstract

Background

Morvan's syndrome is characterized by peripheral nervous system hyperexcitibility (myokymia and neuromyotonia), hyperhydrosis, sleep disorder, limb paresthesias, and encephalopathy. Voltage gated potassium channel antibodies (VGKC abs) are frequently present. Reduplicative paramnesia (RP) has not been reported with this disorder.

Objective

To describe a patient with Morvan's syndrome presenting with RP.

Design

Single case study.

Patient

A 64-year-old man with several years of myokymia and myoclonus with escalating parasomnia and confusion developed the delusion that a replica of his house and its contents existed 40 mi away.

Results

Serum VGKC ab titer was elevated. Neuropsychological testing disclosed executive function and memory deficits. Electromyography demonstrated diffuse myokymia. Treatment with intravenous immunoglobulin and prednisone produced improvement of RP and myoclonus, but not myokymia.

Conclusion

RP may occur in patients with VGKC ab-associated Morvan's syndrome. Both RP and nervous system hyperexcitability may respond to immunotherapy including intravenous immunoglobulin and corticosteroids.

Introduction

Voltage gated potassium channel antibody (VGKC ab)-associated disorders present with a variety of clinical manifestations, including cognitive disturbances with or without signs of peripheral nervous system hyperexcitability (myokymia and neuromyotonia). Morvan's syndrome refers to peripheral nervous system hyperexcitability, subacute encephalopathy, hallucinations, sleep disturbance, and dysautonomia [1], [2], [3]. Non-paraneoplastic limbic encephalitis associated with VGKC ab without peripheral nervous system hyperexcitability has also been described, and usually presents with seizures, encephalopathy, and hyponatremia [1], [2], [4]. Unlike paraneoplastic limbic encephalitis, which usually has a poor prognosis, VGKC ab-related syndromes are potentially responsive to immunomodulatory therapies; corticosteroids, intravenous immunoglobulin (IVIG), and plasmapheresis have resulted in improved cognitive function [1], [2], [4], [5].

Reduplicative paramnesia (RP), a delusional misidentification syndrome characterized by the belief that a place has been reduplicated and the replica exists at another site [6], [7], [8], [9], [10], [11], has not been described with VGKC ab disorders. We describe a man with RP in the setting of VGKC-ab positive Morvan's syndrome.

Section snippets

Case report

A 64-year-old man presented with the belief his home had been reduplicated, confusion, diffusely abnormal muscle movements, parasomnia with vivid dreams, limb parathesias, and 35-pound weight loss. He specifically denied hyperhydrosis although he felt increasingly intolerant of cold and noted frequent subjective fever. He described eight years of muscle cramping that had started in his feet and calves. Three months before presentation, he had an acute ill-defined episode of joint pain and

Comment

We describe a patient with immunotherapy-responsive RP in the setting of VGKC-ab positive Morvan's syndrome. VGKC abs have been implicated in both peripheral and central nervous system disturbances [1], [2], [18]. VGKC ab-associated encephalopathy with or without peripheral nerve hyperexcitibility produces a range of cognitive and behavioral disturbances [1], [3], [4], [19], [20], [21], [22], [23], [24], [25], [26] (Table 2), but RP has not been reported.

The lesion localization responsible for

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