Acquired neuromyotonia after bone marrow transplantation

Demystifying the spontaneous phenomena of motor hyperexcitability

Possessing a discrete functional repertoire, the anterior horn cell can be in one of two electrophysiological states: on or off. Usually under tight regulatory control by the central nervous system, a hierarchical network of these specialist neurons ensures muscular strength is coordinated, gradated and adaptable. However, spontaneous activation of these cells and their axons can result in abnormal muscular twitching. The muscular twitch is the common building block of several distinct clinical patterns, namely fasciculation, myokymia and neuromyotonia. When attempting to distinguish these entities electromyographically, their unique temporal and morphological profiles must be appreciated. Detection and quantification of burst duration, firing frequency, multiplet patterns and amplitude are informative. A common feature is their persistence during sleep. In this review, we explain the accepted terminology used to describe the spontaneous phenomena of motor hyperexcitability, highlighting potential pitfalls amidst a bemusing and complex collection of overlapping terms. We outline the relevance of these findings within the context of disease, principally amyotrophic lateral sclerosis, Isaacs syndrome and Morvan syndrome. In addition, we highlight the use of high-density surface electromyography, suggesting that more widespread use of this non-invasive technique is likely to provide an enhanced understanding of these motor hyperexcitability syndromes.

A pilot study on neurological manifestations and antibodies against antigens in children with hematological and other cancers

BACKGROUND

Paraneoplastic neurological syndromes (PNS) are most commonly recognized in adults with cancer and can often be identified by the presence of serum antibodies to neuronal proteins that are also expressed by the associated tumor. In children: (a) little emphasis is given to the possibility of paraneoplastic neurological involvement; and (b) few studies investigated the presence of anti-neuronal antibodies.

OBJECTIVE

To run a pilot study on the spectrum of PNS and presence of antibodies to neural antigens in children with malignancies.

METHODS

23 children (7 boys; 16 girls, aged 4 months to 16 years) with hematological or other cancers were examined for neurological manifestations and for antibodies to the neuronal antigens that are frequently detected in adult patients with PNS.

RESULTS

Ten of the 23 children had neurological symptoms (and/or positive antibodies): in 6/10 neurological manifestations could be explained by tumor invasion or chemotoxicity or were probably incidental; a child with neuroblastoma developed opsoclonus-myoclonus syndrome without detectable anti-neuronal antibodies; antibodies to a Tr-like cerebellar antigen [associated to no neurological signs and later enuresis], to voltage-gated potassium channels [associated to sensory signs] and to glutamic acid decarboxylase [associated to multifocal myoclonus] were found in one child each. Results were compared with age- and sex-matched control groups.

CONCLUSION

These results suggest that PNS, though surprisingly not so uncommon in children, may be associated with immune responses to distinct neuronal antigens. Further work is needed to determine whether screening for new antibodies to neuronal antigens could be a useful aid in the diagnosis and prognosis of neurological syndromes in children.

Immunology of disorders of neuromuscular transmission

The neuromuscular junction (NMJ) is a prototype synapse and myasthenia gravis is the prototypic antibody-mediated disorder. There are now three other disorders of neuromuscular transmission caused by antibodies to other essential components of the NMJ. Antibodies to the muscle-specific kinase, MuSK, are defining a new form of myasthenia that can be associated with muscle atrophy. Antibodies to voltage-gated calcium channels are responsible for muscle weakness and autonomic dysfunction in the Lambert Eaton myasthenic syndrome. Antibodies to voltage-gated potassium channels are found in patients with a range of disorders affecting the NMJ, the autonomic system or the central nervous system. The pathogenic mechanisms probably depend on the IgG subclass of the antibodies and are only partly shared between the diseases.

Oxaliplatin-induced neurotoxicity: acute hyperexcitability and chronic neuropathy

Oxaliplatin, a platinum-based chemotherapeutic agent, is effective in the treatment of solid tumors, particularly colorectal cancer. During and immediately following oxaliplatin infusion, patients may experience cold-induced paresthesias, throat and jaw tightness, and occasionally focal weakness. We assessed nerve conduction studies and findings on needle electromyography of patients with metastatic colorectal cancer before and during treatment with oxaliplatin. Twenty-two patients had follow-up studies within 48 h following oxaliplatin infusions, and 14 patients had follow-up studies after 3-9 treatment cycles. Repetitive compound muscle action potentials and neuromyotonic discharges were observed in the first 24-48 h following oxaliplatin infusion, but resolved by 3 weeks. After 8-9 treatment cycles, sensory nerve action potential amplitudes declined, without conduction velocity changes or neuromyotonic discharges. The acute neurological symptoms reflect a state of peripheral nerve hyperexcitability that likely represents a transient oxaliplatin-induced channelopathy. Chronic treatment causes an axonal neuropathy similar to other platinum-based chemotherapeutic agents.