Optic neuropathy in Lewis–Summer syndrome: Presentation of a case

Sir,

Multifocal motor neuropathy is an immunomediated condition characterized by weakness and muscular atrophy, absence of sensory and pyramidal signs, in which weakness is caused by a multifocal block of conduction in motor nerves.¹ It has been associated with high titres of antibodies to ganglioside, especially anti-GM1, and it responds adequately to treatment with high doses of intravenous immunoglobulin (IVIG).^2–5 In 1985, Lewis et al. described 5 patients with multifocal acquired demyelinating sensory and motor neuropathy (MADSAM) (Lewis–Miller syndrome) basically affecting the upper limbs, with multifocal conduction block. Subsequently, Parry and Clarke described a similar condition but with pure motor compromise, similar to and confusing with amyotrophic lateral sclerosis. This entity was given the name multifocal motor neuropathy (MMN). This was followed by observations on the association of this condition with high titres of anti-GM13 antibodies, and evident recovery of muscle strength in most patients with the administration of IVIG. Segmentary demyelinization implies damage to the myelinic membrane or Schwan's cell, with less important involvement of the axon. It usually appears in immunologically mediated demyelinization or in alterations of myelin metabolism. Myelin may also be affected through myelinotoxic agents or mechanically by compression. This kind of patient poses problems when it comes to achieving a correct diagnosis: is it a case of axonal or demyelinizing neuropathy? And if we reach a diagnosis of demyelinizing neuropathy, is it acquired or hereditary? These questions must be answered in the clinical course, electrophysiological analysis, study of the cerebrospinal fluid, immunological tests, biopsy of the nerve and genetic studies.

Axonal polyneuropathies are usually treatment-resistant, probably because the treatment is inadequate or because the process of recovery through regeneration is very slow or incomplete, habitually associated with metabolic or toxic diseases. For this reason, achieving the definition of a polyneuropathy as demyelinizing after ruling out hereditary causes suggests a pathology capable of being treated. Acquired demyelinizing neuropathies represent a heterogeneous group, generally immunologically mediated. Chronic demyelinizing inflammatory polyneuropathy is the most common cause.²

We report the case of a 61-year-old male attending the emergency department due to loss of visual acuity in his right eye over a period of 48 h. We conducted a complete ophthalmological examination in which visual acuity in that right eye allowed finger-counting while the left eye had 10/10. An afferent pupil defect was observed, while nothing abnormal was found on examination of the fundus oculi by means of mydriasis. The patient was therefore suspected of having retrobulbar optic neuritis and ER staff requested an analysis and GSV, all completely normal, and a campimetry which showed a generalized depression in sensitivity in the right eye, while the left eye was completely normal. He was initially prescribed boluses of corticosteroids and we started to study the patient with the neurology department. During anamnesis, the patient reported the presence of progressive muscle weakness, especially in the upper body, lasting for years, and that he had been operated for a pinched nerve in an upper limb without any improvement, but which he had ignored. The diagnosis was approached thanks to the electromyographic study (in which we were to find nerve conduction block in two or more nerves, altered sensory conduction velocity and abnormal sensory responses. It is difficult to reach a diagnosis with respect to other polyneuropathies, particularly with multifocal motor neuropathy, because it is complicated to demonstrate conduction block).^6,7 The magnetic resonance scan requested revealed demyelinization lesions. A lumbar puncture was performed, with the protein level that was found to be normal and a complete analysis showed no evidence of AntiGM1.^2–4 He achieved scant or no recovery of his eyesight, even though the bolus steroid treatment was continued as it has been shown to be effective in some cases, and treatment was also begun with immunoglobulins and the patient's course has been monitored.

The difficulties in diagnosing demyelinizing polyneuropathies range from the clinical picture to the electrophysiological pattern,^6,7 thus requiring the performance of additional complementary examinations or even inadequate or unnecessary treatments. On the other hand, all the international diagnostic criteria must be taken into account with caution, individualizing each case; although they show high specificity, they do not present great sensitivity, leaving patients without adequate treatment.