Electrodiagnosis of botulism

Guidelines for single fiber EMG

This document is the consensus of international experts on the current status of Single Fiber EMG (SFEMG) and the measurement of neuromuscular jitter with concentric needle electrodes (CNE - CN-jitter). The panel of authors was chosen based on their particular interests and previous publications within a specific area of SFEMG or CN-jitter. Each member of the panel was asked to submit a section on their particular area of interest and these submissions were circulated among the panel members for edits and comments. This process continued until a consensus was reached. Donald Sanders and Erik Stålberg then edited the final document.

Longitudinal neurophysiological assessment of intramuscular type-A botulin toxin in healthy humans

The aim of this study is to assess the neurophysiological abnormalities of type A botulin toxin-infiltrated human muscle, and their evolution over time. Seried cMAP measurements, 3 and 20 Hz repetitive nerve stimulation, EMG, SFEMG over 3 months from toxin injection. Our findings consist in lack of decrement with 3 Hz repetitive nerve stimulation and facilitation with 20 Hz repetitive nerve stimulation; progressive increasing of jitter; early appearance of fibrillations; small and short motor unit action potential in the first 3 weeks, followed by increasing of MUAP amplitude and duration, with polyphasic morphology. Although claimed as highly specific and sensible, neuromuscular junction facilitation is an inconstant finding in human botulism. Therefore, lack of neuromuscular junction facilitation cannot exclude a diagnosis of botulism. Our findings are compatible with a process of acute denervation followed by distal reinnervation, favored by terminal nerve sprouting.

Electrodiagnosis of disorders of neuromuscular transmission

This article reviews the use of electrodiagnostic testing in disorders of neuromuscular transmission and discusses the differences between various presynaptic and postsynaptic disorders. Attention is paid to quality control issues that influence the sensitivity of repetitive nerve stimulation and single fiber electromyography. Electrodiagnostic testing, when used as an extension of the clinician's history and physical examination, will provide appropriate direction in establishing the diagnosis.

Infant botulism

Infant botulism results from the absorption of heat-labile neurotoxin produced in situ by ingested Clostridium botulinum. Honey and environmental exposure are the main sources of acquisition of the organism. Clinical manifestations are owing to progressive neuromuscular blockade, initially of muscles innervated by cranial nerves and later of the trunk, extremities and diaphragm. Presynaptic autonomic nerves are also affected. The diagnosis is made on clinical grounds and is confirmed by recovery of the organism or by detection of toxin in the stool. Management includes meticulous supportive intensive care that may include mechanical ventilation and administration of human botulinum immunoglobulin in severe cases.

Guillain-Barré syndrome: perspectives with infants and children

An acute flaccid paraparesis or ascending quadriparesis in an infant or child constitutes a very important pediatric neurology emergency. The Guillain-Barré syndrome (GBS) is the most frequent cause. This is primarily an autoimmune, post-infectious, demyelinating, peripheral nervous system process. A small percentage of children develop a primary axonal process not unlike that identified more commonly in China. Because of the potential for acute respiratory compromise, any child suspected of having GBS needs immediate hospitalization. The major considerations in differential diagnosis include transverse myelitis, toxic neuropathies, tick paralysis, infantile botulism, myasthenia gravis, and dermatomyositis. On occasion, some younger children present with an acute severe pain syndrome that may mask as a pseudo-encephalopathy. Another clinical variant is the Miller-Fisher syndrome characterized by ataxia, ophthalmoparesis, and areflexia. This is associated with a high frequency of the anti-GQ-1-b antibodies. Although most children with GBS have a relatively benign clinical course, some become very ill and require intubation with intensive care monitoring. Immunomodulating treatment should be used for any child who loses the ability to walk. To date, no well-controlled study has been completed analyzing the relative merits of the two most commonly used therapies, namely plasmapheresis or intravenously administered immunoglobulin.

Clinical spectrum of botulism

Botulism is a paralyzing disease caused by the toxin of Clostridium botulinum. The toxin produces skeletal muscle paralysis by producing a presynaptic blockade to the release of acetylcholine. Recent studies have pinpointed the site of action of the several types of botulinum neurotoxin at the nerve terminal. Since the discovery of the toxin about 100 years ago, five clinical forms of botulism have been described: 1) classic or foodborne botulism; 2) wound botulism; 3) infant botulism; 4) hidden botulism; 5) inadvertent botulism. A clinical pattern of descending weakness is characteristic of all five forms. Almost all human cases of botulism are caused by one of three serotypes (A, B, or E). Classic and wound botulism were the only two forms known until the last quarter of this century. Wound botulism was rare until the past decade. Now there are increasing numbers of cases of wound botulism in injecting drug users. Infant botulism, first described in 1976, is now the most frequently reported form. In infant botulism spores of Clostridium botulinum are ingested and germinate in the intestinal tract. Hidden botulism, the adult variant of infant botulism, occurs in adult patients who usually have an abnormality of the intestinal tract that allows colonization by Clostridium botulinum. Inadvertent botulism is the most recent form to be described. It occurs in patients who have been treated with injections of botulinum toxin for dystonic and other movement disorders. Laboratory proof of botulism is established with the detection of toxin in the patient's serum, stool, or wound. The detection of Clostridium botulinum bacteria in the stool or wound should also be considered evidence of clinical botulism. Electrophysiologic studies can provide presumptive of botulism in patients with the clinical signs of botulism. Electrophysiologic testing can be especially helpful when bioassay studies are negative. The most consistent electrophysiologic abnormality is a small evoked muscle action potential in response to a single supramaximal nerve stimulus in a clinically affected muscle. Posttetanic facilitation can be found in some affected muscles. Single-fiber EMG studies typically reveal increased jitter and blocking, which become less marked following activation. The major treatment for severe botulism is advance medical and nursing supportive care with special attention to respiratory status.

Neuro-ophthalmic findings in botulism type B

In June 1989, the largest recorded outbreak of food-borne botulism occurred in the United Kingdom. Twenty-seven patients were affected during the outbreak with type B botulism. A case note review of 14 patients admitted with this condition was performed and the neuro-ophthalmic findings are presented. Patients with severe disease presented with a combination of ocular and bulbar symptoms; in mild cases dysphagia was noted first and visual disturbance followed within 24 hours. Clustering of cases and bilaterality of cranial nerve signs aided in the diagnosis. Accommodative paresis and sixth cranial nerve palsy were frequent early signs. When there was respiratory paralysis and ventilatory failure, it occurred within 12 hours of the onset of a third cranial nerve palsy.