LONG‐TERM EFFECT OF INTRAVENOUS IMMUNOGLOBLIN THERAPY (IVIg) IN MULTIFOCAL MOTOR NEUROPATHY (MMN)

Abstract

Terenghi F., Casellato C., Cappellari A., Meucci N., Carpo M., Bersano A., Priori A., Barbieri S., Scarlato G., Nobile‐Orazio E.Department of Neurological Sciences, Milan University, IRCCS Ospedale Maggiore Policlinico, Milan Italy.We studied the long‐term effect of high dose intravenous immunogloblin therapy (IVIg) in 21 patients with multifocal motor neuropathy (MMN) initially treated with a standard dose of 2g/kg over 4 to 5 consecutive days followed by periodic maintenance infusion (1g/kg over 2 consecutive days) at the time of clinical worsening. Clinical assessment of response was performed in all patients before and 8–10 days after the initial IVIg course, then yearly during follow‐up using: 1) MRC scale for muscle strength in 20 muscles of the upper and lower limbs (maximal score 200); 2) functional impairment scales for upper and lower limbs; and 3) modified Rankin disability scale. In all patients nerve conduction studies were performed before and 8–10 days after the initial treatment, then periodically during follow‐up. After the initial IVIg course 15 patients (71%) consistently and 5 (24%) marginally improved while one did not respond. The mean MRC sum‐score raised from 165 to 176 after IVIg. At last follow‐up, after 1–10 years (mean 5.5) of maintenance infusions, the percentage of patients remaining improved was reduced to 33%. The mean MRC sum‐score at last follow‐up was similar (164) to pre‐treatment value. The disability scores for upper and lower limbs improved in 16 and 9 patients, respectively, with a successive worsening at last follow‐up in 4 and 5 of them. The Rankin score improved in 12 patients with a successive worsening in 6. During follow‐up most patients needed higher IVIg dosage to maintain improvement even if in two this increase did not prevent worsening. Before IVIg, conduction blocks (CB) were found in 34 nerves (20 definite, 6 probable and 8 possible) and low distal CMAP amplitude in 24 of 136 examined. We selected 51 nerves (24 with CB) for the electrophysiological follow‐up studies: 10 CB disappeared while 10 new CB were detected in other sites (1 definite, 2 probable and 7 possible); low distal CMAP were found at onset in 10 nerves in 4 of which they further decreased, and appeared in 14 others nerves. The mean distal CMAP at follow‐up consistently decreased from initial values (17 vs 6.5 mV). This study confirms that IVIg is highly effective as initial treatment in MMN although its efficacy tends to decrease during time concurrently with the appearance of axonal degeneration.