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Readers of the editorial by Wokke and van den Berg1 may be left with the impression that the immunoglobulins could provide hope for the future for patients with pure lower motor neuron syndromes but no conduction block. Their evaluation of the results obtained by Ellis et al 2 in four of the total series of 10 patients may tend towards overoptimism, however.
We agree with their second conclusion regarding the criteria for referring this subgroup of patients with lower motor neuron disease to a highly specialised centre for further analysis. However, we would recommend referral for all patients with motor neuron disease, especially in cases in the initial stages or in atypical forms, in which the diagnosis may be difficult if strict criteria are applied, given the complexity and multidisciplinary management of this condition and the difficulty of the decision regarding when and to whom pharmacological and life sustaining therapy should be applied.
Great care must be taken to avoid misdiagnosis in the selection of candidates for therapy, as the high cost of long term treatment does not justify indiscriminate immunoglobulin use. A critical reading of work of Ellis et al shows that only three responding patients of the 10 treated presented an objective improvement in the pinch and grip myometries and no statistically significant modification in the MRC scale or significant objective improvement in the paired t test was found.
Finally, of the 10 patients with lower motor neuron syndrome included in the assay, there were four cases of amyotrophic lateral sclerosis (ALS), one of spinal muscular atrophy (SMA), one doubtful case of multifocal motor neuropathy (MMN), and four probable cases of MMN at follow up. These last five presented no conduction blocks and only one had anti-GM1 antiganglioside antibodies.
If we accept and if we can demonstrate the usefulness of immunoglobulins in lower motor neuron forms, two questions arise. Firstly, can we accept the existence of MNN without conduction block? Katz et al tried to answer this question by proposing that conduction block was only one of many electrodiagnostic features in a segmental demyelination. They advocated the inclusion of other features, such as conduction velocity, temporal dispersion, delayed F wave responses, and prolonged distal latencies
Ellis et al admit that their study was not designed as an electrophysiological study, and that the exhaustive nerve conduction studies described by Lang et al and Katz et al were not performed.3 4 Secondly, if we accept that we are dealing with patients lower motor neuron disease, we would have to re-examine the hypothesis that has been considered to be flawed regarding the role played by immune mechanisms in motor neuron diseases.5
Another point about which we have our reservations is that it cannot be affirmed that the non-introduction of this treatment leaves the patients at the mercy of the disease's natural course. The problem lies in the difficulty in diagnosing these patients, especially those who present neither conduction blocks nor anti-GM1 antiganglioside antibodies. As we have previously stated, the final diagnosis in 50% was ALS or SMA. Given these results, it seems more reasonable to persist with differential diagnosis by magnetic resonance neurography and repetition of neurophysiological examinations, including magnetic transcortical stimulation.
Patients with motor neuron disease and their relatives, who have been anxiously waiting for a breakthrough in treatment, have been disappointed time and again in recent years by promises regarding therapies that have been both expensive and of little use. It can only be hoped that the immunoglobulins will improve this situation, and that our scepticism is mistaken.
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