Does the MUNIX Method Reflect Clinical Dysfunction in Amyotrophic Lateral Sclerosis: A Practical Experience

The aim of our study was to assess the usefulness of the MUNIX method in reflecting the clinical dysfunction in patients with amyotrophic lateral sclerosis (ALS), as well as to assess an intra-rater reproducibility of MUNIX. The study group consisted of a total of 15 ALS patients. The mean age of symptoms onset was 55 years, and the mean disease duration was 10 months. The muscle strength and patients’ functional status were assessed according to the Medical Research Council (MRC) and by ALS functional rating scale revised (ALSFRS-R), respectively. The MUNIX was performed in 6 muscles: abductor pollicis brevis (APB), abductor digiti minimi (ADM), biceps brachii (BB), tibial anterior (TA), extensor digitorum brevis (EDB), and abductor hallucis (AH), unilaterally, at a less affected side. Both muscle-specific and global MRC and MUNIX scores were calculated. In 11 patients, the study protocol was repeated at least twice every 3 months. An additional testing of the intra-rater reliability was performed at the first visit. There were no significant differences between MUNIX test and re-test values in the APB, ADM, BB, TA, EDB, and AH muscles (P >0.05). The highest variability of the test–retest values was found in the BB muscle (7.53%). Although there was a significant test–retest difference in the global MUNIX score (P = 0.02), the variability of the results was as low as 1.26%. The MUNIX value correlated with the muscle-specific MRC score in ABP, ADM, TA, EDB and AH (P <0.05), and the global MUNIX values correlated with global MRC scores (P <0.05). There was also a significant correlation between the global MUNIX score and the clinical dysfunction measured by the ALSFRS-R scale (P <0.05). The global MUNIX showed a higher monthly decline (4.3%) as compared with ALFRS-R (0.7%) and the MRC global score (0.5%). This study confirms that the MUNIX method is a sensitive, reliable, and accurate tool reflecting both motor dysfunction and disease progression in ALS. We have found this approach to be more reliable and technically easier in distal muscles with less atrophy and a better strength.