By Michael Rubin, MD
Professor of Clinical Neurology, Weill Cornell Medical College
Dr. Rubin reports no financial relationships relevant to this field of study.
SYNOPSIS: Electrodiagnostic criteria using nerve conduction velocities are useful to distinguish most hereditary neuropathies from acquired neuropathies in children.
SOURCE: Potulska-Chromik A, Ryniewicz B, Aragon-Gawinska K, et al. Are electrophysiological criteria useful in distinguishing childhood demyelinating neuropathies? J Peripheral Nervous System 2016:21:22-26.
Using electrodiagnostic criteria in the pediatric population, is it possible to distinguish chronic inflammatory demyelinating polyneuropathy (CIDP) from hereditary forms of demyelinating neuropathy, including Charcot Marie Tooth 1a (CMT1a), the most common form of CMT, caused by a PMP22 gene duplication, and hereditary neuropathy prone to pressure palsy (HNPP), caused by a PMP22 gene deletion? Lacking biological markers, CIDP diagnosis relies heavily on nerve conduction studies (NCS) and cerebrospinal fluid analysis, both difficult to perform in children, and identifying sensitive and specific NCS parameters would be clinically advantageous.
Retrospective analysis was undertaken of 18 CIDP patients, seven HNPP patients, and 24 CMT1a patients, diagnosed between 2002-2014 at the Pediatric Neuromuscular Unit, Department of Neurology, Medical University of Warsaw, Poland. All had onset of symptoms prior to age 18 years. Nerve conduction studies were performed in the standard fashion and analyzed using at least four sets of diagnostic criteria, including those formulated by the American Academy of Neurology and the European Federation of Neurological Societies/Peripheral Nerve Society.
Among CIDP patients, distal compound muscle action potential (CMAP) duration was longer than 9 ms in at least one nerve in 77% (14 of 17), and motor conduction block of > 30% was found in 88% (16 of 18), mostly (83%) not at common entrapment sites. Supportive criteria for acquired neuropathy was present in 50% (9 of 18), comprising: 1) a 10 m/s conduction velocity difference between two corresponding nerves in the arms or legs; 2) an abnormal terminal latency index (TLI), calculated as the distal conduction distance (mm)/(conduction velocity (m/s) x distal motor latency (ms); 3) abnormal median sensory but normal sural sensory response; or 4) the converse, abnormal sural sensory but normal median sensory response.
Among seven HNPP patients, none had a distal CMAP duration > 9 ms, and partial motor conduction block was found in only 28% (2 of 7), all at common sites of entrapment (ulnar nerve at elbow, peroneal nerve at fibular head). Among 24 CMT1a patients, prolonged distal CMAP duration in at least one nerve was seen in 58% (n = 14), and motor conduction block was found in 25% (n = 5). Other than an abnormal TLI in two patients, none had any supportive criteria for acquired neuropathy.
Distal CMAP duration > 9 ms in at least one nerve, abnormal median sensory but normal sural sensory response, and a 10 m/s conduction velocity difference between two corresponding nerves in the arms or legs are strong indicators of pediatric CIDP, differentiating it from HNPP and CMT1a.
COMMENTARY
Most childhood neuropathies are genetic in origin. Acquired neuropathies are usually inflammatory, with CIDP representing only 3% of pediatric neuropathies, most of which occur prior to 10 years of age, and 20% of which present as Guillain-Barre syndrome. As in adults, childhood CIDP is more frequent in males, with prevalence of approximately 0.48/100,000 in children compared to 7.7/100,000 in adults. Consequent to the IVIG CIDP Efficacy (ICE) trial, intravenous immunoglobulin (IVIG) has become the treatment of choice for CIDP, although plasma exchange and corticosteroids are equally efficacious.1 Children respond well to IVIG, as well as to corticosteroids. Azathioprine, in combination with steroids, constitutes a third-line alternative. Approximately 25% obtain long-term remission after discontinuation of immunotherapy, while 45% may require a year or more of regular infusions, given at a dose of 1 g/kg every 3-4 weeks.
REFERENCE
- Hughes RA, Donofrio P, Bril V, et al. Intravenous immune globulin (10% caprylate-chromatography purified) for the treatment of chronic inflammatory demyelinating polyradiculoneuropathy (ICE study): A randomized placebo-controlled trial. Lancet Neurol 2008;7;136-144.
Electrodiagnostic criteria using nerve conduction velocities are useful to distinguish most hereditary neuropathies from acquired neuropathies in children.
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