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Plasmapheresis is a well established therapy in immunogenic peripheral neuropathies.1 However, patients with multifocal motor neuropathy do not respond very well to prednisone or plasmapheresis.2 This case report illustrates that plasmapheresis may even be disadvantageous in multifocal motor neuropathy.
Muscle strength was assessed (MRC scale) and a sum score was calculated from 10 sites (bilateral shoulder abduction, extension of hands and fingers, hip flexion, dorsal flexion of feet); full muscle strength meaning a sum score of 50.
Nerve conduction studies were carried out according to the method described elsewhere.3 Compound muscle action potentials (CMAPs) were recorded from abductor digiti minimi and tibialis anterior bilaterally by surface electrodes. Ulnar nerves were stimulated supramaximally with surface electrodes at the wrist, distal elbow, proximal elbow, axilla, Erb's point, C7 vertebra; peroneal and sciatic nerve at head of fibula, sciatic notch, and L1 vertebra by a Digitimer high voltage D180 stimulator (Digitimer Ltd, Welwyn Garden City, England).
Plasmapheresis was carried out by a standard polypropylene filter P2S (Fresenius, Germany) with a maximum pore diameter of 0.5 μm. This filter separates immunoglobulins. Three litres were exchanged against human albumin (5% on each of 3 consecutive days (12, 13, 14 November 1998)).
The patient had given fully informed consent for both nerve conduction studies and treatment.
The male patient was born in 1931. In 1979 distal atrophic weakness developed in his right shoulder and hand muscles. There were no sensory symptoms. His CSF and neuroradiology were normal; electromyography showed a chronic neurogenic lesion. Vasculitis had been excluded by sural nerve biopsy. The diagnosis of spinal muscular atrophy was made. In 1993, when the patient was first seen here, he had complete paresis of his right arm, paretic left hip flexion (MRC 4), and peroneal weakness in his left leg with slightly impaired position sense in the toes. No weakness was found in the left arm and right leg. Muscle stretch reflexes were absent in the right arm and both legs. There were no central signs. In 1993 GM1 antibodies were positive (serum titre 1/200) and remained positive until 1998 (December 1998, GM1-antibodies 29 U/ml, limit of normal 25 U/ml). In 1993 muscle sum score was 34 and conduction block was seen in the proximal right ulnar nerve between Erb's and axilla and in both proximal sciatic nerves between L1 and the sciatic notch. His CSF was normal again. Multifocal motor neuropathy was diagnosed, and the patient was put on intravenous immunoglobulin (IVIg) with 180 g SandoglobinRinitially—followed by 100 g IVIg every fortnight. Within two weeks muscle strength improved. The patient was able to use his right arm, strength in his left leg improved, and position sense became normal (muscle sum score 42 in 1996). Intermittent deterioration was treated with oral methylprednisolone (1994–6 (4 mg a day); 1996–8 (2 mg a day)) which had a subjective effect on muscle strength. Additional cyclophosphamide had to be withdrawn because it was not tolerated very well. In 1998 muscle strength gradually deteriorated under 100 g IVIg every 2 weeks. Muscle weakness became more pronounced in the proximal right arm (MRC 2–3) and left foot dorsiflexion (MRC 1); sum score was 36 in August 1998. Therefore, it was decided to give three courses of plasmapheresis. Before plasmapheresis muscle sum score was 36 and the patient was able to walk. Plasmapheresis was performed on 12-14 November 1998. On 14 November muscle strength started to deteriorate. On 17 November the patient became tetraplegic with a disability sum score of 19. His left arm and right leg, which had not been weak before, were paretic with shoulder abduction MRC 4, hip flexion MRC 2. There was proximal conduction block in both ulnar and sciatic nerves (figure). The patient received 120 g IVIg immediately (17–19 November) and 60 g IVIg on 24–25 November. Muscle strength improved gradually. On 30 November he was able to stand. On 11 December—after another three courses of 50 mg IVIg—he could walk with a stick, but he was still unable to use his right hand and to climb stairs. Treatment was continued with 50 g IVIg a week and 50 mg cyclophosphamide a day. By the end of January 1999 the patient had regained his former muscle strength. He was able to walk without a walking aid, to climb stairs, and he could use his right hand (sum score 36). Increasing CMAPs after proximal nerve stimulation (figure) paralleled clinical improvement.
This follow up study illustrates that deterioration can be seen under continuing treatment with IVIg. Additionally, plasmapheresis may stimulate antibody rebound, and cause substantial deterioration in multifocal motor neuropathy. It is assumed that it is not only antibodies which are responsible for conduction block and muscle weakness that are washed out by plasmapheresis but also those which act at the lesion site by blocking the pathogenic agent. In this patient, before plasmapheresis, serum gammaglobulin was increased at 2.32 g/dl (12 November); thereafter it was 0.7g/dl (18 November), and recovered to 1.79 g/dl (24 November).
It has been shown that serum of patients with multifocal motor neuropathy can block stimulus conduction in distal motor nerves.4 This could be due to an effect on sodium channel function in the distal motor nerve. Furthermore, the rapid clinical improvement after IVIg could be due to an interference of IVIg with the blocking effect of antibodies on the sodium channels at the motor nerve endings.5 It is unlikely that plasmapheresis caused acute demyelination in our patient. In plasmapheresis, antibodies, complement, and cytokines are removed; therefore, this case supports the hypothesis4 of a complement independent effect of antibodies on sodium channel function in the distal motor nerve.
Even with good clinical results the pathogenic process of multifocal motor neuropathy may remain active under the treatment with IVIg for many years. Therefore, muscle weakness develops if immunoglobulins are washed out by plasmapheresis.