Optical neuropathy in Lewis-Summer syndrome: A casual relationship?

Dear Editor:

It was with great interest that we read the clinical case published in your journal under the title “Optic neuropathy in Lewis-Sumner syndrome: Presentation of a case”.¹ We expected to read about a nosological link between central demyelinating disease in optic neuropathy and the peripheral demyelinating disease that characterises Lewis-Sumner syndrome (LSS). At the very least we thought the authors would have envisaged this possibility, upon finding both pathologies in the same patient. Instead, we found a short (but interesting) review of neuropathies with conduction block mentioning both multifocal motor neuropathy (MMN) and LSS. The differences between the two syndromes may not have been sufficiently emphasised. LSS is currently considered an asymmetric or multifocal type of chronic inflammatory demyelinating polyneuropathy (CIDP). Unlike in MMN, the sensory fibres are affected, finding anti-GM1 antibodies is uncommon, and a significant number of cases of this disease respond favourably to corticosteroid treatment.^2,3 Nevertheless, this therapeutic response has been called into question by a recent study proposing that LSS be clearly distinguished not only from MMN, but also from CIDP.⁴ Lastly, regarding the case mentioned in the letter by Sánchez Ferreiro and Barreiro González, impairment of the central nervous system has been described in LSS, but as far as we know, not in MMN.^5–7 In the case recently mentioned in NEUROLOGÍA,¹ the authors describe the co-presence of LSS and retrobulbar optic neuritis in the same patient. However, neither of the pathologies is completely illustrated: no EMG results are given, and the pathogenesis of the optic neuritis is not clearly explained, since the authors list no vascular or autoimmune tests and do not specify the anatomical structure in which the magnetic resonance scan revealed demyelinating lesions. Above all, the authors’ intent to establish an aetiopathogenic association between the two illnesses is never fully clarified. We therefore wonder if Sánchez Ferreiro and Barreiro González, in their letter to the editor, meant only to report the presence of two unusual pathologies in the same patient (pathologies which, furthermore, were not correctly described), or if they meant to suggest that the co-presence of two demyelinating diseases might be due to more than a mere chance. If the latter is true, the authors have unfortunately failed to transmit the interesting points of this case and their possible hypothesis.