3 Cases of MMN

MMN autoimmune by:Dr Imran Khan, |JUNE 29, 2020

Below are three diverse cases of MMN described effecting hand and foot.

Multifocal Motor Neuropathy

Motor neuropathy & lower motor neurone part-3

Go to MMF Discussion page What is Multi Focal Neuropathy

3. Illustrative cases

CASE 1:  42 year old woman with weakness in the right hand for a year was referred for motor neuron disease. During the next year the hand weakness became severe and involved first the left hand and then the left foot. Physical examination revealed distal asymmetric weakness .There was weaknes sin left hand without atrophy. Tendon reflexes were 1+ throughout. Sensory testing showed reduction in vibratory sensation at the toes. Electrodiagnostic studies showed motor conduction block in the median nerves bilaterally between the elbow and wrist. Nerve conduction velocities were normal. Sensory nerves were normal. Serum IgM anti-GM1 antibodies were present in high titer (3,900; normal <600).
During the next 10 months there was progressive weakness and loss of reflexes despite high dose prednisone therapy and 11 treatments with plasma exchange. Six monthly treatments with two plasma exchanges followed by intravenous cyclophosphamide (1 gm/M2 ) were followed by improvement, beginning after 3 to 4 months, and progressing to nearly normal strength over the next year. She remained stable, off all medications, for 3 years. She then noted mild recurrent weakness in the right hand in a distribution similar to that at disease onset 5 years before.

COMMENT: Asymmetric weakness, developing distally in an arm or hand, is the most common pattern of early involvement in MMN. Reflexes are often normal early in the disease course. Significant sensory signs are rare, but patients occasionally note symptoms such as paraesthesias, or even abnormal taste sensations. Prednisone treatment is rarely effective, and is often associated with rapid exacerbations of weakness. The decision to use cyclophosphamide was only made when 1. it became clear that the patient had developed significant disability, and 2. there were clear signs that an immune disorder was present, including conduction block and high serum titers of IgM anti-GM1 antibodies. Improvement in strength after cyclophosphamide begins late, often 3 to 6 months after beginning therapy, and continues for up to a year after the end of the treatment course

CASE 2:A 52 year old male noted a right foot drop. During the next 6 months weakness and cramps became progressively worse in the right leg and also developed in the left leg. On examination there was asymmetric weakness, predominantly in the legs. Muscle tone was normal. Cranial nerves were normal. Tendon reflexes were absent at the right ankle, but 2+ elsewhere. Sensation was normal. Electrodiagnostic testing showed denervation in thoracic paraspinous muscles and both lower extremities. Nerve conduction velocities were normal. No serum anti-GM1 antibodies were detected.

COMMENT: This patient has  acute  weakness with  lower, motor neurons involvement. The clinical course is rapid .. The diagnosis progressive muscular atrophy, or,  lower motor neuron syndrome. Such patients may not develop bulbar, or upper motor neuron, signs and never meet diagnostic criteria for ALS. Denervation in the thoracic paraspinous muscles is more suggestive of a motor neuron disease than a motor neuropathy. With no evidence of demyelination or serum antibodies to suggest an immune etiology for the syndrome, it is likely that this patient will have continued progression of weakness that does not respond to immunosuppressive treatments.A 55 year old man was referred for possible immunosuppression to treat a lower motor neuron syndrome with anti-GM1 antibodies. He had noted  difficulty climbing stairs and arising from a chair for 10 to 15 years. His speech  become slurred and he needed more time to eat.  Neurological testing showed weakness and fasciculations of the tongue and face. The tongue showed severe atrophy. Moderate symmetric, proximal weakness was present. Tendon reflexes were zero. Sensation was reduced to all modalities distally in the feet. Electrodiagnostic testing showed chronic denervation, most prominent in the face, tongue, and proximal muscles. Repeat anti-GM1 antibody testing showed a pattern of polyreactive serum IgM binding to GM1 ganglioside and to histone H3 at titers of about 1,500.

COMMENT: The patients weakness was proximal and symmetric, more typical of inherited motor neuron disorders than of acquired motor neuropathies. Although the patient had high titers of anti-GM1 antibodies, the pattern of binding was polyreactive. Polyreactive antibodies are not specific for immune motor syndromes, and are also found in 3% to 5% patients with ALS and adult-onset spinal muscular atrophies. Further testing revealed an excessive number of trinucleotide repeats in the androgen receptor, a finding consistent with X-linked hereditary bulbo-spinal muscular atrophy. This case emphasizes that determination of the specificity of anti-GM1 antibodies helps to determine their clinical relevance. The polyreactive antibodies in a patient with features atypical of a motor neuropathy were not, of themselves, an indication for immunosuppressive therapy.

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