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ARTICLES: E. Delmont, J. P. Azulay, R. Giorgi, S. Attarian, A. Verschueren, D. Uzenot, and J. Pouget Multifocal motor neuropathy with and without conduction block: A single entity? Neurology 2006; 67: 592-596 [Abstract] [Full text] [PDF]

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Multifocal motor neuropathy with and without conduction block: A single entity?

Daniel L Menkes   (25 October 2006)

Reply from the Authors

Emilien Delmont, Jean-Philippe Azulay, Sharam Attarian, Annie Verschueren, David Uzenot, Jean Pouget   (25 October 2006)

Multifocal motor neuropathy with and without conduction block: A single entity? 25 October 2006
Daniel L Menkes, UTHSC at Memphis 855 Monroe Ave., Link Bldg Rm 415, Memphis, TN 38163 Send Correspondence to journal: Re: Multifocal motor neuropathy with and without conduction block: A single entity? dmenkes{at}utmem.edu Daniel L Menkes	Delmont et al's recent report [1] provides a compelling case that motor neuropathies responsive to IvIg may not demonstrate conduction block [CB] on conventional nerve conduction studies, [NCS]. Drs. Chaudry and Swash concurred with a previous report that distal demyelination with secondary axon loss may be responsible for this finding.[2,3] Both publications advocate an empiric IvIg in those patients in whom there is an index of suspicion for an immune-mediated motor neuropathy. However, IvIg is costly, may be in short supply, and may produce significant side effects. A previous report of 31 patients proposed a set of criteria by which a high likelihood of response to IvIg could have been predicted based upon a clinical examination, a CSF examination and an assessment for proximal conduction block. [4] If two of three were present, then there was a 95% chance that the patient would respond to IvIg. Perhaps the authors have these data. CB often manifests motor weakness out of proportion to atrophy whereas axon loss should manifest as weakness with proportional atrophy. The authors comment on muscle atrophy but they did not specifically comment upon this relationship. Did all their patients manifest motor weakness out of proportion to bulk and tone in affected muscles with an MRC grade > 3? Furthermore, did these patients manifest needle EMG recruitment patterns suggestive of demyelination wherein there was early recruitment of very few units that had an increased firing frequency? Delmont et al admit that they did not perform additional studies that may have identified proximal conduction block. However, they did identify patients with F waves prolonged into the demyelinating range. Abnormal spontaneous activity with a normal cervical MRI would provide further support for their hypothesis of proximal conduction block with secondary axon loss at root level. Did these authors examine the cervical paraspinal muscles in these patients in addition to obtaining a cervical spine MRI? As albuminocytologic dissociation is uncommon in patients with motor neuronopathies, what percentage of patients in total had an elevated CSF protein? More specifically, what number of patients had at least one of the following; an examination suggestive of demyelination, inferred root level demyelination, and an elevated CSF protein? If all of Delmont et al’s patients had a least one of these findings then perhaps treating neurologists should restrict empiric trials of IvIg to patients with lower motor neuron syndromes manifesting at least one of these criteria. References 1 Delmont E, Azulay JP, Giorgi R et al. Multifocal motor neuropathy with and without conduction block- a single entity? Neurology 2006; 67:592-596. 2 Chaudhry V, Swash M. Multifocal motor neuropathy-is conduction block essential? Neurology 2006; 67:558-559. 3 Menkes DL. Axonal multifocal motor neuropathy without conduction block or other features of demyelination. Neurology 2002; 59:1666. 4. Menkes DL, Hood DC, Ballesteros RA, and Williams DA. ”Root stimulation aids in the detection of acquired demyelinating polyneuropathies.” Muscle Nerve 1998; 21:298-308. The authors report no conflicts of interest.
Reply from the Authors 25 October 2006
Emilien Delmont, Service de Neurologie, Hôpital Pasteur Pavillon F, 30 Avenue de la Voie Romaine 06002 Nice, France, Jean-Philippe Azulay, Sharam Attarian, Annie Verschueren, David Uzenot, Jean Pouget Send Correspondence to journal: Re: Reply from the Authors emilien.delmont{at}wanadoo.fr Emilien Delmont, et al.	We thank Dr. Menkes for his thoughtful comments. We did not conclude that that IVIg treatment must be given to all motor neuron diseases. [1] This treatment must be tested in selected patients presenting features of a multifocal motor neuropathy (MMN) whatever conduction blocks are present or not. Features suggestive of demyelination support the diagnosis of undetected conduction block. These criteria are clinical, biological and electrophysiological. Weakness in a peripheral nerve distribution and absence of bulbar, respiratory and upper motor neuron involvement are suggestive of a MMN. The main biological criteria is a high titer of anti-GM1 antibody. Considering the nerve conduction study, delayed F waves latencies and delayed distal latencies suggest a demyelinating process even in absence of conduction block. Other techniques can be used to detect proximal conduction block, such as nerve root stimulation [4], conventional transcranial magnetic stimulation and triple stimulation technique [5], and brachial plexus MRI. [6] Absence of muscle atrophy relatively to weakness is a good clinical sign of suspected demyelination, but it is a subjective evaluation without any quantitative data. A motor weakness with a peripheral nerve distribution on clinical and electrophysiological examination is to us a more objective argument for a MMN rather than for a lower motor neuron syndrome. Elevated CSF protein is a good criteria of demyelination in CIDP. It is rare in MMN with conduction block and it is not a predictive factor of response to IVIg. [7] We did not perform additional studies for proximal conduction block in this study [1], but we did it in another study. [5] Ten patients with motor neuropathies without conduction block had conventional transcranial magnetic stimulation and triple stimulation technique and, in seven patients, proximal conduction block were confirmed or temporal dispersion which were associated with a satisfactory response to IVIg. This technique is less painful and invasive than root stimulation. Presence of conduction block is not required to treat patients with a typical pattern of motor weakness if a peripheral nerve distribution is present on clinical and electrophysiological evaluation. The entity of multifocal motor neuropathy without conduction block is probably not a single entity based on our evaluation of proximal nerve segments by transcranial magnetic stimulation [5] and based on our study [1] that did not find any significant difference between multifocal motor neuropathies with conduction block and without conduction block. References 5. Attarian S, Azulay JP, Vershueren A, Pouget J. Magnetic stimulation using a triple stimulation technique in patients with multifocal neuropathy without conduction block. Muscle Nerve 2005; 32: 710-714. 6. Van Es HW, Van den Berg LH, Franssen H. Magnetic resonance imaging of the brachial plexus in patients with multifocal motor neuropathy. Neurology 1997; 48: 1218-1224. 7. Van den Berg-Vos RM, Franssen H, Wokke JHJ, Van Es HW, Van den Berg LH. Multifocal motor neuropathy: diagnostic criteria that predict the response to immunoglobulin treatment. Ann Neurol 2000; 48: 919-926. Disclosure: The authors report no conflicts of interest.