Peripheral nerve hyperexcitability

Neuromyotonic and myokymic discharges are abnormal electrical muscular discharges caused by ectopic discharges from motor axons and represent the hallmarks of peripheral nerve hyperexcitability. Neuromyotonic discharges are specific for peripheral nerve hyperexcitability syndromes, whereas myokymic discharges may occur either focally or in a more generalized fashion in many other peripheral nerve disorders. Isaacs syndrome and Morvan syndrome are rare acquired peripheral nerve hyperexcitability disorders that share common clinical features and are often associated with elevated voltage-gated potassium channel-complex antibodies. Central nervous system symptomatology is more common in Morvan syndrome, which also overlaps with limbic encephalitis. Cramp-fasciculation syndrome, a more common syndrome, may represent a milder form of peripheral nerve hyperexcitability. Peripheral nerve hyperexcitability syndromes should be distinguished from stiff person syndrome, myotonic disorders, and rippling muscle disease. When severe, Isaacs syndrome and Morvan syndrome may be disabling but often respond to membrane-stabilizing drugs and immunomodulatory treatments. The electrophysiologic features of these disorders are described.

Overlooked non-motor symptoms in myasthenia gravis

Patients with myasthenia gravis (MG) may have various non-motor symptoms in addition to fatigability and weakness of skeletal muscles. Thymomas contain abundant immature thymocytes and developing CD4 and CD8 T cells. Thymomas are found in 15-25% of patients with MG and are associated with severe symptoms. We suggest that non-motor symptoms are based on the autoimmune disorders probably owing to an abnormal T cell repertoire from thymomas. Using previously reported cases and cases from our multicentre cooperative study, we review the clinical characteristics of patients with thymoma-associated MG who have non-motor symptoms. CD8 T cell cytotoxicity against haematopoietic precursor cells in bone marrow and unidentified autoantigens in hair follicles lead to the development of pure red cell aplasia, immunodeficiency and alopecia areata. In contrast, neuromyotonia, limbic encephalitis, myocarditis and taste disorders are autoantibody-mediated disorders, as is MG. Autoantibodies to several types of voltage-gated potassium channels and the related molecules can evoke various neurological and cardiac disorders. About 25% of patients with thymoma-associated MG have at least one non-motor symptom. Non-motor symptoms affect many target organs and result in a broad spectrum of disease, ranging from the impairment of quality of life to lethal conditions. Since relatively little attention is paid to non-motor symptoms in patients with thymoma-associated MG, the symptoms may be overlooked by many physicians. Early diagnosis is important, since non-motor symptoms can be treatable. A complete understanding of non-motor symptoms is necessary for the management of patients with thymoma-associated MG.

[Isaacs's syndrome and associated diseases]

Isaacs' syndrome is an antibody-mediated potassium channel disorder. Clinical symptoms of Isaacs' syndrome are characterized by muscle cramp, slow relaxation following muscle contraction, and hyperhidrosis. Hyperexcitability of the peripheral nerve cause these symptoms, which are relieved by administration of Na channel blockers and immunotherapy.The target channel proteins are voltage-gated potassium channels (VGKCs). The suppression of voltage-gated outward K(+) current by antibodies induces hyperexcitability of the peripheral nerve. Electrophysiological findings show that antibodies may not directly block the kinetics of VGKCs, but may decrease channel density. From the electrophysiological, pharmacologic and immunologic view points, the site of origin of spontaneous discharges is located principally in the distal portion of the motor nerve."VGKC antibodies" are also detected in Morvan syndrome (severe insomnia with neuromyotonia and various autonomic disorders) and in a form of autoimmune limbic encephalitis. Recent studies indicated that the "VGKC antibodies" are mainly directed toward associated proteins (for example LGI-1, CASPR-2) that complex with VGKCs themselves. The "VGKC antibodies" are now usually known as VGKC-complex antibodies. In general, LGI-1 antibodies are most common in limbic encephalitis with SIADH. CASPR-2 antibodies are present in the majority of patients with Morvan syndrome.

[A case of Tolosa-Hunt syndrome presenting ocular neuromyotonia]

A 27-year-old woman noticed diplopia when gazing left and paresthesia of the left face and headache of the left side for 8 months. Abduction and supraduction of the left eye were moderately restricted. Hypoesthesia of the face innervated by the ophthalmic branch of the left trigeminal nerve was detected. Visual disturbance due to optic neuropathy developed 5 months later. MRI with gadolinium revealed a mass lesion extending from the left cavernous sinus to the orbital apex. Ocular neuromyotonia and corresponding diplopia were induced by sustained right gaze. Such episodes occurred almost every day on awaking in the morning. Prednisolone (60 mg/day) was given and the headache and visual disturbance ameliorated in two days. The diplopia disappeared in 4 days. The patient remains free from these symptoms after 6 months. This is the first report of ocular neuromyotonia associated with Tolosa-Hunt syndrome.

Frostbite-like skin lesion as an autonomic symptom of Isaacs' syndrome

A 25-year-old woman complained of numbness of the extremities, following muscle rigidity and tenderness. The presence of anti-voltage-gated potassium channel antibody led to the diagnosis of Isaacs' syndrome. Twenty-seven months after the first symptom, she developed a pricking pain sensation in the lateral left foot, and then gradually developed a purple skin lesion resembling frostbite. The lesion completely disappeared 2 days later. An incidental episode occurred at the same site 8 months later. Frostbite-like skin lesions may be a rare autonomic manifestation in Isaacs' syndrome.

Nerve excitability studies characterize Kv1.1 fast potassium channel dysfunction in patients with episodic ataxia type 1

Episodic ataxia type 1 is a neuronal channelopathy caused by mutations in the KCNA1 gene encoding the fast K(+) channel subunit K(v)1.1. Episodic ataxia type 1 presents with brief episodes of cerebellar dysfunction and persistent neuromyotonia and is associated with an increased incidence of epilepsy. In myelinated peripheral nerve, K(v)1.1 is highly expressed in the juxtaparanodal axon, where potassium channels limit the depolarizing afterpotential and the effects of depolarizing currents. Axonal excitability studies were performed on patients with genetically confirmed episodic ataxia type 1 to characterize the effects of K(v)1.1 dysfunction on motor axons in vivo. The median nerve was stimulated at the wrist and compound muscle action potentials were recorded from abductor pollicis brevis. Threshold tracking techniques were used to record strength-duration time constant, threshold electrotonus, current/threshold relationship and the recovery cycle. Recordings from 20 patients from eight kindreds with different KCNA1 point mutations were compared with those from 30 normal controls. All 20 patients had a history of episodic ataxia and 19 had neuromyotonia. All patients had similar, distinctive abnormalities: superexcitability was on average 100% higher in the patients than in controls (P < 0.00001) and, in threshold electrotonus, the increase in excitability due to a depolarizing current (20% of threshold) was 31% higher (P < 0.00001). Using these two parameters, the patients with episodic ataxia type 1 and controls could be clearly separated into two non-overlapping groups. Differences between the different KCNA1 mutations were not statistically significant. Studies of nerve excitability can identify K(v)1.1 dysfunction in patients with episodic ataxia type 1. The simple 15 min test may be useful in diagnosis, since it can differentiate patients with episodic ataxia type 1 from normal controls with high sensitivity and specificity.

[Immune-mediated neuromyotonia (Isaacs' syndrome)--clinical aspects and pathomechanism]

Neuromyotonia occurs due to several causes such as hereditary, immune-mediated and degenerative neurological disorders. Isaacs' syndrome (immune-mediated neuromyotonia) is an antibody-mediated potassium channel disorder (channelopathy). Clinical symptoms of Isaacs' syndrome are characterized by muscle cramp, slow relaxation following muscle contraction (pseudomyotonia), and hyperhidrosis; these symptoms are due to hyperexcitability of the peripheral nerve, including autonomic nerve. These symptoms are relieved by the administration of Na channel blocker and immunotherapy. Recent studies show that this disease is not infrequently associated with neoplasm, especially thymoma. The target channel proteins of the antigens are voltage-gated potassium channels (VGKCs), specifically dendrotoxin-sensitive fast potassium channels. The suppression of voltage-gated outward K+ current by antibodies induces the hyper- excitability of the peripheral nerve. The findings of patch clamp studies show that antibodies may not directly block the kinetics of VGKCs, but may decrease channel density. From the electrophysiologic, pharmacologic and immunologic view points, the site of origin of spontaneous discharges is located principally in the distal portion of the motor nerve and/or within the terminal arborization. Anti-VGKC antibodies were also found to be positive in patients with Morvan's syndrome, limbic encephalitis and temporal epilepsy. Thus, an increasing number of immune-mediated neurological disorders with anti-VGKC antibodies are being identified. However, except in Morvan's syndrome, it is rare to find symptoms pertaining to involvement of both the peripheral and central nervous system in the same patient with anti-VGKC antibodies. The differences in the pathomechanism of Isaacs' syndrome and limbic encephalitis are still unclear.

Serial monitoring of basal metabolic rate for therapeutic evaluation in an Isaacs' syndrome patient with chronic fluctuating symptoms

A 52-year-old man presented with hyperhydrosis, painful pseudomyotonia and gait disturbance. The condition was diagnosed as Isaacs' syndrome on the basis of characteristic findings noted on an electromyogram. Carbamazepine treatment was only partially and transiently effective. Intravenous immunoglobulin therapy was effective. The basal metabolic rate (BMR) was serially monitored using an automatic integrated system for breath analysis. Serial monitoring of the BMR facilitates therapeutic evaluation in an Isaacs' syndrome patient with chronic fluctuating symptoms.

Acquired neuromyotonia in childhood: case report and review

Recently characterized as an immune-mediated channelopaty, Isaacs' syndrome (also known as acquired neuromyotonia) was first described in 1961 in two men with persistent, generalized muscle stiffness, in addition to spontaneous, rapid discharges of motor-unit potentials on electromyography. In the peripheral nervous system, antibodies targeted to voltage-gated potassium channels induce hyperexcitability of motor axons, resulting in signs of muscle stiffness or of pseudomyotonia. A spontaneous burst of single motor-unit activity, and myokymic and neuromyotonic discharges, are the most characteristic features found in electromyography studies. This report describes Isaacs' syndrome in a child, in whom the diagnosis was made by clinical features of acquired, spontaneous muscle overactivity and typical electromyographic findings.

Interspike interval analysis in a patient with peripheral nerve hyperexcitability and potassium channel antibodies

Neuromyotonia or Isaacs' syndrome is a rare peripheral nerve hyperexcitability disorder caused by antibodies against potassium channels of myelinated axons. We present the high-density surface electromyographic (EMG) recordings of a patient with fasciculations and cramps due to neuromyotonia. To characterize the time course of hyperexcitability, we analyzed the interspike intervals (ISIs) between fasciculation potentials, doublet, and multiplet discharges. ISI duration increased within each burst. The ISI histograms found can be explained by the recovery cycle of the myelinated axon and its dependency on the slow potassium conductance. We conclude that ISI analysis is a useful tool to understand the membrane dynamics underlying abnormal motor unit activity.

[Case of Isaacs' syndrome associated with Hashimoto disease]

We report a case of Isaacs' syndrome associated with Hashimoto disease. A 26-year-old woman, who had a past history of Hashimoto disease, complained of involuntary movements and muscle cramp in lower extremities. On examination, myokymia was seen in lower extremities. Myokymia was observed even during sleep, and worsened by exercise or bathing. The antibody against voltage-gated potassium channel (VGKC) was positive. Myokymic discharges were recorded with needle EMG in lower extremities. The patient was diagnosed as having Isaacs' syndrome. Isaacs' syndrome tends to be associated with some other autoimmune diseases. We discussed the correlation between Isaacs' syndrome and autoimmune disease. About 23% of Isaacs' syndrome cases are associated with some other autoimmune diseases and myasthenia gravis was most common. This is the first case report of Isaacs' syndrome associated with Hashimoto disease in Japan.

Inherited neuromyotonia: A clinical and genetic study of a family

Neuromyotonia is a disorder of peripheral nerve hyperexcitability characterized by myokymia, muscle cramps and stiffness, delayed muscle relaxation after contraction (pseudomyotonia), and hyperhidrosis, associated with well described spontaneous electromyographic features. It is usually an acquired disorder associated with autoantibodies against neuronal voltage-gated potassium channels. However, mutations of KCNA1, encoding the K(+) channel subunit hKv1.1, have been reported in rare families with neuromyotonia, and mutations in KCNQ2, encoding voltage-gated potassium M channel subunit, in families with benign neonatal seizures and myokymia. We report a three-generation family with inherited neuromyotonia without evidence of immunological involvement. Genetic study excluded mutations in KCNA1, KCNA2, KCNA6 and KCNQ2 genes. Our study does not completely exclude the involvement of other genes encoding ion channels subunits in the pathogenesis of this disorder. Further studies of familial cases will shed light on the molecular basis of inherited neuromyotonia.

Primary Aberrant Regeneration and Neuromyotonia of the Third Cranial Nerve

A 52-year-old woman presented with episodic diplopia with a duration of 6 months. Between the episodes, infraduction of the right eye was mildly impaired with retraction of the right upper lid on downgaze. On resuming the primary position after prolonged left gaze, she developed a right esotropia and reduced abduction, supraduction, and infraduction of the right eye. There was no history of cranial radiation or previous diagnosis of a brain lesion. Brain imaging results were negative. The interictal infraduction deficit and lid retraction were interpreted as signs of a mild right third cranial nerve palsy with primary aberrant regeneration. The episodic esotropia and ductional deficits were considered to be signs of neuromyotonia. This combination of findings, rarely described before, suggests a link between primary aberrant regeneration and neuromyotonia. Abnormal and excessive conduction triggered by stimulation of a partially damaged nerve probably underlies ocular neuromyotonia.

Isaacs' syndrome associated with myasthenia gravis, showing remission after cytoreductive surgery of pleural recurrence of thymoma

We report a patient with Isaacs' syndrome associated with myasthenia gravis and pleural recurrence of thymoma, who showed severe limb pain attributed to hyperexcitability of sensory nerves. Myokymia and severe pain were successfully treated with cytoreductive surgery and intraoperative hyperthermic intrathoracic perfusion chemotherapy, but neither pharmacotherapy nor plasma exchange showed obvious clinical effects. Pleural thymoma in our patient may have caused Isaacs' syndrome, probably by unconfirmed humoral immune mechanisms. Cytoreductive treatment for recurrent thymoma should be actively considered as a potent therapeutic option in refractory patients with disabling neuromyotonia symptoms.

Neuromyotonia

Neuromyotonia is a rare condition of spontaneous and continuous muscle fibre activity of peripheral nerve origin. It represents the more severe phenotype of peripheral nerve hyperexcitability, and when acquired is often associated with antibodies to voltage-gated potassium channels. There are no specific published electromyographic or clinical diagnostic criteria for this disorder. This review highlights the classical clinical, electrophysiological and immunological features of this disorder from what is currently known in the literature to date, and also from the author's own patients' studies. Neuromyotonia is best classified as a moderately severe disorder of peripheral nerve hyperexcitability, with electromyographic features of spontaneous, continuous, irregularly occurring doublet, or multiplet single motor unit (or partial motor unit) discharges, firing at a high intraburst frequency (30-300Hz). Invariably, patients develop persistent muscle contraction, often worse following exercise. About 40% of patients with acquired neuromyotonia will have detectable voltage-gated potassium-channel antibodies. Clinical, electrophysiological and immunological measurements are important in defining the phenotype of neuromyotonia, and other, milder forms of peripheral nerve hyperexcitability.

IgM-containing fraction suppressed voltage-gated potassium channels in acquired neuromyotonia

OBJECTIVES

Acquired neuromyotonia (ANM) is an autoimmune disorder caused by antibodies to voltage-gated potassium channels (VGKC). Previously, we reported a patient with immunoglobulin M (IgM), instead of immunoglobulin G (IgG), anti-VGKC antibody. The purpose of this study was to determine the function of IgM-containing fraction in ANM patients.

MATERIALS AND METHODS

We determined whether anti-VGKC antibodies in the IgG or IgM-containing fractions suppressed outward potassium current (OKC) using the patch clamp method in three patients with ANM. Whole sera from all patients suppressed OKCs.

RESULT

Only the purified IgG, not the IgM-containing fractions from two patients suppressed VGKCs, whereas in a patient with IgM anti-VGKC antibody, only the IgM-containing fractions, not the IgG-containing fractions suppressed VGKCs.

CONCLUSION

Anti-VGKC antibodies belonging to the IgM subclass should be determined in seronegative ANM patients.

Sequential antibodies to potassium channels and glutamic acid decarboxylase in neuromyotonia

A patient with thymoma-associated neuromyotonia and voltage-gated potassium channel (Kv1.2 and Kv1.6) antibodies by immunoprecipitation and rat brain immunolabeling was treated successfully with immunoadsorption and cyclophosphamide. Curiously, glutamic acid decarboxylase antibodies, absent at onset, appeared later. Stiff-person syndrome was absent, but fast blink reflex recovery suggested enhanced brainstem excitability. The range of antibodies produced in thymoma-associated neuromyotonia is richer, and the timing of antibody appearance more complex, than previously suspected.

Isaacs' syndrome: Clinical and electrophysiological response to gabapentin

A patient with Isaacs' syndrome had generalized muscle spasms, twitching, and progressive muscle stiffness for 21 years. Electrodiagnostic study showed continuous spontaneous motor-unit activity and the presence of M-wave afterdischarges. He responded dramatically to treatment with carbamazepine but developed a drug rash; his treatment was changed to gabapentin with continued improvement. Subsequent nerve conduction studies showed decreased amplitude and later an absence of M-wave afterdischarges. Gabapentin thus appears to be an effective treatment for Isaacs' syndrome.

Finger flexion resembling focal dystonia in Isaacs' syndrome

We describe a patient with a 5-month history of gradually progressive painless flexion of the left ring finger associated with cramps in both thighs. She has severe chronic obstructive pulmonary disease and was on salbutamol. Serum anti-voltage-gated potassium channel antibodies was positive. Electromyography showed generalized neuromyotonia and myokymic discharges. The cramps were partially relieved by phenytoin. We would like to highlight that finger flexion resembling dystonia can be a presenting sign of Isaacs' syndrome.

Neuromyotonia with neuropathy and muscle hypertrophy: association or cause?

Continuous muscle fibre activity in a patient with demyelinating neuropathy is rare. We report an 18 year old boy who presented with walking difficulty and continuous rippling in muscles of upper and lower limbs. He had dysarthric speech, hypertrophied arm and calf muscles with normal power, tone, reflexes and sensations. Myokymic discharges were seen in deltoid, biceps, quadriceps and calf muscles. His blood counts, chemistry, thyroid profile, DNA, Rh factor were normal and CPK was raised. CSF showed protein 50 mg/dl and 4 lymphocyte/mm3. Nerve conduction study revealed conduction block and absence of peroneal F wave. EMG showed neuromyotonic discharges which disappeared on regional neuromuscular blocker but not on nerve block or general anaesthesia. He responded partially to prednisolone. Acquired demyelinating neuropathy may result in neuromyotonia and muscle hypertrophy which may partially respond to prednisolone.

Neuromyotonia: Clinical profile of twenty cases from northwest India

OBJECTIVES

We are presenting 20 cases of the intriguing clinico-electromyographic entity, now considered a potassium channel disorder, Neuromyotonia. Our experience with the clinical manifestations, underlying abnormalities and response to various therapies is documented.

MATERIALS AND METHODS

Patients with diffuse pain or undulating muscle movements, with or without stiffness were sent for electromyographic and further studies. Patients with "neuromyotonic discharges" were included after exclusion of hypocalcaemia.

RESULTS

Our cases included 19 males and one female of age group 15 to 52 years, the majority being between 30 to 45 years. Undulating movements were seen in 19, of which two had focal twitching. Muscle stiffness was a complaint in five; pain was the chief presenting complaint of 19, which started in the calf in all. Irritability, insomnia and a peculiar worried pinched face were present in 12 patients. CSF was abnormal with mildly raised protein in eight. Curiously, 11 of these patients had taken ayurvedic treatment for various complaints in the preceding one month. Bell's palsy was associated in four, peripheral neuropathy in two and residual poliomyelitis in two. Electromyographic evidence of spontaneous activity in the form of "neuromyotonic discharges" was seen in all. Antibodies to voltage gated potassium channels was tested in one patient and was positive (titer was 1028 pM). Membrane stabilizers (e.g, phenytoin sodium) in our experience did not provide adequate rapid relief; we tried high-dose intravenous Methylprednisolone in 19 with significant amelioration of complaints. One patient was offered intravenous immunoglobulin, to which he responded.

CONCLUSIONS

Neuromyotonia is a heterogeneous condition and can present in varied ways including diffuse nonspecific pain. This uncommon condition is potentially treatable and can be picked up with high index of suspicion.

Clinical electrophysiological characterization of the acquired neuromyotonia phenotype of autoimmune peripheral nerve hyperexcitability

Acquired autoimmune neuromyotonia is regarded as part of the spectrum of peripheral nerve hyperexcitability disorders. We aimed to use clinical neurophysiological measurements to study the extent, distribution, and characteristics of spontaneous motor unit potentials in 11 patients with acquired neuromyotonia. Investigations revealed that most spontaneous discharges recorded were motor unit, or partial motor unit potentials of normal size. Bursts of motor unit potentials arose more commonly from distal portions of the peripheral nerve and had abnormal absolute and relative refractory periods. Spontaneous discharges in some patients occurred in semirhythmic bursts in certain muscles. No patient had neurophysiological abnormalities detectable in first-order neurons of the central nervous system when using transcranial magnetic stimulation to estimate the threshold for corticomotor excitation and determine central motor conduction time. Only patients with coexistent myasthenia gravis had neurophysiologically detectable defects in neuromuscular transmission. The pathogenic region of abnormality in peripheral nerve hyperexcitability disorders therefore seems to lie within the terminal branches of peripheral motor nerves.

Continuous motor unit activity syndromes: a video-polysomnographic study

OBJECTIVE

To ascertain the presence of abnormalities of sleep in patients with continuous motor unit activity with and without symptoms of central nervous system involvement.

METHODS

Five patients with isolated neuromyotonia (Isaacs' syndrome) and 1 patient with Morvan syndrome underwent 24-h videopolysomnographic recording to investigate sleep structure, motor activities and autonomic variables during sleep.

RESULTS

Macro- and microstructural organization of sleep and of the attending autonomic variables were substantially normal in patients with Isaacs' syndrome. On the contrary, sleep structure was severely disrupted with subcontinuous dream enactment and hallucinations in the patient with Morvan syndrome. The pattern of the neuromyotonic discharges, however, was not different between the patients with Isaacs' syndrome compared to Morvan syndrome, the EMG discharges persisting throughout the 24 h of recording and affecting wakefulness and sleep equally.

CONCLUSIONS

Neuromyotonia is compatible with normal organization of sleep. The severe sleep abnormalities observed in Morvan syndrome cannot be simply attributed to the effects of neuromyotonia of peripheral origin.

SIGNIFICANCE

Even though neuromyotonia is common to both Isaacs' and Morvan syndromes, the two conditions differ significantly in regard to CNS involvement with sleep abnormalities and lumping the two conditions together is not justified on clinical and neurophysiological grounds.

The origin of spontaneous discharges in acquired neuromyotonia. A Macro EMG study

OBJECTIVE

To study the generator sites of spontaneous discharges in patients with immune-mediated neuromyotonia.

METHODS

Macro EMGs triggered by both spontaneously and voluntarily activated single action potentials were recorded and the mean peak-to-peak amplitude and area of the macro motor unit potentials were compared in two patients with typical acquired neuromyotonia having positive antibodies against voltage-gated potassium channels.

RESULTS

Mean peak-to-peak amplitude and area of Macro EMG motor unit potentials (macro MUPs) triggered by spontaneous discharges were significantly smaller than those triggered by voluntary activation in both patients. However, a few macro MUPs triggered by spontaneous discharges resembled those triggered by voluntary activation.

CONCLUSIONS

Spontaneous discharges in two patients with immune-mediated neuromyotonia seem to be mostly generated at sites distal to the terminal axon branching points.

SIGNIFICANCE

This finding may provide a new insight in the understanding of spontaneous discharges in immune-mediated neuromyotonia.

Thymoma-associated neuromyotonia with antibodies against voltage-gated potassium channels presenting as chronic intestinal pseudo-obstruction

Chronic intestinal pseudo-obstruction can occur as a paraneoplastic disorder, and several cases have been reported in association with thymoma or small-cell lung cancer. Autoantibodies against voltage-gated potassium channels (VGKCs) are found in acquired neuromyotonia (Isaac's syndrome), and have been reported in one case of slow transit constipation without apparent neurological disease. We describe a patient with VGKC antibodies, acquired neuromyotonia and thymoma, who first presented with a severe slow-transit constipation and in whom the gastrointestinal symptoms responded well to plasmapheresis. We suggest that VGKC antibodies might be helpful in patients with possible paraneoplastic chronic intestinal pseudo-obstruction, and a positive result should stimulate the search for a thymoma or other tumour and raise the possibility of immunotherapy.

Expanding the phenotype of potassium channelopathy: severe neuromyotonia and skeletal deformities without prominent Episodic Ataxia

We report an unusual family in which the same point mutation in the voltage-gated potassium channel gene KCNA1 resulted in markedly different clinical phenotypes. The propositus presented in infancy with marked muscle stiffness, motor developmental delay, short stature, skeletal deformities, muscle hypertrophy and muscle rippling on percussion. He did not experience episodic ataxia. His mother presented some years later with typical features of Episodic Ataxia type 1 (EA1), with episodes of ataxia lasting a few minutes provoked by exercise. On examination she had myokymia, joint contractures and mild skeletal deformities. A heterozygous point mutation in the voltage-gated K(+) channel (KCNA1) gene (ACG-AGG, Thr226Arg) was found in both. We conclude that mutations in the potassium channel gene (KCNA1) can cause severe neuromyotonia resulting in marked skeletal deformities even if episodic ataxia is not prominent.

Immunological features of neurological paraneoplastic syndromes

Neurological paraneoplastic syndromes are a rare group of disorders that occur in 1-2% of people with malignancy. They are usually caused by an immune response, triggered by and directed against a tumour, that cross-reacts with protein expressed by the peripheral or central nervous system. Any part of the nervous system can be affected and patients often develop severe and permanent disability. Diagnosis can be difficult as in two-thirds of patients the neurological problems appear up to 5 years before the tumour manifests. However, certain of these syndromes are often associated with specific serum autoantibodies that can be useful both in diagnosis of the neurological syndrome and in focusing the search for a particular tumour. Thus, these antibodies can allow earlier identification and treatment of cancer and, potentially, a reduction in morbidity and mortality. It was only in the 1980s that the first anti-neuronal autoantibodies were characterized and their associations with clinical syndromes and tumours defined. Further antibodies have been isolated over the past 20 years and novel pathogenic mechanisms for several syndromes have been recognized. For example, voltage-gate ion channels seem to be a common target for autoantibodies involved in peripheral nerve diseases such as the Lambert-Eaton myasthenic syndrome and neuromyotonia (Isaacs' syndrome). However, the place of most paraneoplastic antibodies in the pathogenesis of central syndromes is yet to be fully elucidated.

[Isaacs' syndrome, stiff person syndrome and Satoyoshi disease: pathomechanisms and treatment]

Neurological disorders with characteristic clinical manifestations of painful muscle cramp and stiffness are not infrequent. The immune-mediated mechanism with specific antibodies among these diseases is particularly important for treatment. Isaacs' syndrome (acquired neuromyotonia) is an antibody-mediated potassium channelopathy. The suppression of voltage-gated potassium channel (VGKC) by antibodies induces peripheral nerve hyperexcitability. Antibodies may decrease VGKC density by cross-linking F (ab)2 fractions and increasing the degradation rate of VGKCs. Stiff person syndrome (SPS) and its variants show characteristic symptoms and signs of central nervous system hyperexcitability due to antibodies to the GABA-ergic system such as glutamic acid decarboxylase (GAD), amphiphysin 1 and gephyrin. The role of GAD is the subject of debate, however, recent studies reveal the intrathecal synthesis of GAD which is specific for SPS and appears to impair GABA synthesis. Satoyoshi disease is characterized by painful muscle cramp, baldness, intractable diarrhea, bone and joint deformity, and endocrine disturbances. Muscle cramp may be due to inhibition of the spinal interneuron and hyperexciatability of the anterior horn cell. In patients with Satoyoshi disease, sera reacted with an 85 kDa protein of human brain lysate. In all these disorders, suppression or removal of specific antibodies is critical, however, the effects are short-lived, and supplemental treatment to reduce the hyperexcitability of the peripheral or central nervous system will be needed.

Myokymia, neuromyotonia, dermatomyositis, and voltage-gated K+ channel antibodies

A young woman presented with facial myokymia in association with dermatomyositis. There was no evidence of peripheral neuropathy. Needle electromyography showed prominent myokymic discharges and brief neuromyotonic discharges in addition to many small-amplitude, short-duration motor unit potentials. Myokymia and dermatomyositis both responded to immunosuppressive treatment. The presence of antibodies to voltage-gated potassium channels and the association with dermatomyositis indicated an autoimmune cause for myokymia, which may have been due to reversible peripheral nerve hyperexcitability.

Isaacs' syndrome as a potassium channelopathy of the nerve

Isaacs' syndrome (acquired neuromyotonia) is an antibody-mediated potassium channel disorder (channelopathy). The target channel proteins of the antigens are voltage-gated potassium channels (VGKCs), especially dendrotoxin-sensitive fast potassium channels. The suppression of voltage-gated outward K(+) current by antibodies induces hyperexcitability of the peripheral nerve. Patch clamp studies show that antibodies may not directly block the kinetics of VGKCs but may decrease channel density. Electrophysiological, pharmacological, and immunological findings indicate that the site of origin of spontaneous discharges is principally in the distal portion of the motor nerve and/or within the terminal arborization. The spectrum of potassium channelopathies is expanding. The existence of antibodies against VGKCs should be considered in patients who present with generalized nerve hyperexcitability of undetermined etiology.

Acute oxaliplatin-induced peripheral nerve hyperexcitability

PURPOSE

Oxaliplatin is a novel platinum compound with clinical activity in several malignancies. Neurotoxicity is dose-limiting and occurs in two distinct forms, an acute neurologic symptom complex that occurs within hours or days of therapy and a chronic, cumulative sensory neuropathy.

PATIENTS AND METHODS

Patients were treated in a phase I study designed to establish the maximum-tolerated dose of capecitabine given with oxaliplatin. Because of the unusual neurosensory toxicity of oxaliplatin, detailed neurologic examination, needle electromyography (EMG), and nerve conduction studies (NCS) were performed before and the day after oxaliplatin in a subset of 13 patients. Carbamazepine therapy was tried in 12 additional patients to determine whether the neurologic effects might be relieved.

RESULTS

All patients experienced acute, reversible neurotoxicities with oxaliplatin. Symptoms included paresthesias, dysesthesias, cold hypersensitivity, jaw pain, eye pain, pain in the arm used for drug infusion, ptosis, leg cramps, and visual and voice changes. Serial EMG and NCS revealed striking signs of hyperexcitability in motor nerves after oxaliplatin. In patients who achieved therapeutic levels, carbamazepine did not alter the clinical or electromyographic abnormalities.

CONCLUSION

The acute neurotoxicity seen with oxaliplatin is characterized by peripheral-nerve hyperexcitability, and the findings are similar to the clinical manifestations of neuromyotonia. Carbamezepine, which provides symptomatic relief in acquired neuromytonia, did not seem to be beneficial. Efforts to identify a successful neuroprotectant strategy would have a major impact on improving patient quality of life and the ability to deliver full doses of oxaliplatin.

[A case of Isaacs' syndrome associated with dextrocardia]

INTRODUCTION

Isaacs syndrome is a disorder of unknown etiology characterized by muscular rigidity, cramps and myokymias. Described by Isaacs in 1961 and called by him as continuous muscular activity syndrome. There are few reports in Latino american countries.

CLINICAL CASE

A 31 year-old man with sustained muscular contractions in lower limbs and diffuse myokymias since he was eighteen-year old. Dextrocardia was disclosed on clinical examination.

CONCLUSION

We report the case of a patient with Isaacs syndrome and dextrocardia.

Acquired neuromyotonia and peripheral neuropathy in a patient with Hodgkin's disease

Acquired neuromyotonia is characterized by hyperexcitability of motor nerves resulting in continuous muscle fiber activity. It occurs most often as a paraneoplastic syndrome in patients with cancers of the immune system. Antibodies against voltage-gated potassium channels (VGKCs) have been detected in some patients. Peripheral neuropathy is sometimes present. We report on a patient with Hodgkin's lymphoma in complete remission who developed paresthesias followed by neuromyotonia with bulbar involvement. Peripheral sensorimotor neuropathy was diagnosed electrophysiologically and evidence of axonal degeneration and demyelination was detected by sural nerve biopsy. The patient's complaints, including dysarthria, improved after carbamazepine treatment.