MPS-MUNE and MUNIX on abductor pollicis brevis (APB) were done at week-1 and week-4 of symptom onset in 10 AIDP patients (mean age: 50.10) and in 22 healthy controls (mean age: 49.82). Motor unit size was calculated as surface-Motor-Unit-Potential (sMUP) and Motor-unit-size-index (Musix). Electromyography of APB was performed in all patients.
In AIDP patients, MPS-MUNE (week-1: 85 (18-193), week-4: 87 (18-158)) and MUNIX (week-1: 113 (23-256), week-4: 124 (26-187)) differed from control MPS-MUNE (141 (66-329) and MUNIX (203 (116-364)) (p < 0.01, Kruskal-Wallis-rank-test). SMUP and Musix in AIDP did not differ from controls. MPS-MUNE and MUNIX did not change from week-1 to week-4. Electromyography of APB showed only slight denervation in two patients while MUP analysis was normal in all.
Decreased MPS-MUNE and MUNIX already at week-1 in AIDP patients suggest loss of functioning axons rather than motor unit loss because of lacking denervation activity and reinnervation in most patients.
MUNE methods may provide valuable information to understanding the disease pathophysiology and follow-up of AIDP.