L. Andersen

Two- and 6-minute walk tests assess walking capability equally in neuromuscular diseases.

Objective: This methodologic study investigates if the 2-minute walk test (2MWT) can be a valid alternative to the 6-minute walk test (6MWT) to describe walking capability in patients with neuromuscular diseases. Methods: Patients (n = 115) with different neuromuscular diseases were invited to participate on 2 test days, each consisting of 1 2MWT and 1 6MWT separated by a minimum 30-minute period of rest. The order of the walk tests was randomly assigned via sealed envelopes. A group of 38 healthy controls completed 1 6MWT. Results: The mean walking distance for the 2MWT was 142.8 meters and for the 6MWT 405.3 meters. The distance walked in the 2MWT was highly correlated to the distance walked in the 6MWT (r = 0.99, p < 0.001). There was a significant decrease in walking speed from the first to last minute in the 6MWT, both among patients and healthy controls, which was not evident in the 2MWT. Results were consistent across diagnoses and levels of disease severity. Conclusion: The 2MWT is a potential alternative to the 6MWT to describe walking capability among patients with neuromuscular diseases during clinical trials.

The 2- and 6-Minute Walk Tests in Neuromuscular Diseases: Effect of HeartRate Correction on the Learning Effect

Objective: The 2- and 6-minute walk tests are common measures for evaluating walking ability, but reliability is weakened by a well-documented learning effect. Since heart rate is related to workload, any change in walking distance, which is unrelated to change in clinical function, should be reflected in a change in heart rate during walking. Therefore, the aim of the present study was to investigate test-retest reliability of the 2- and 6-minute walk tests with and without heart rate correction. Methods: Ninety-three adult patients (mean age of 53 years, range; 22-83 years) with 12 different neuromuscular diseases (myotonic dystrophy type 1, limb-girdle muscular dystrophy, facioscapulohumeral muscular dystrophy type 1, Charcot-Marie-Tooth disease, mitochondrial myopathy, Becker muscular dystrophy, spinobulbar muscular atrophy, sporadic inclusion body myositis, spinal muscular atrophy, myotonia congenita Thomsen disease, congenital myopathy, polymyositis) were recruited in the study. One 2- and 6-minute walk test was performed on two occasions, 1-2 weeks apart. Heart rate was monitored by a pulse-watch. Results: The distance walked increased significantly with repeated 2- and 6-minute walk tests (2-minute walk test increased by 4 ± 9 m and 6-minute walk test by 11 ± 26 m, p<0.001). Heart rate correction eliminated the learning effect in the 6-minute walk test (+0.01 m/heartbeat, p=0.84), but not in the 2-minute walk test (+0.03 m/ heartbeat, p=0.018). The same pattern of heart rate-correction in the 6-minute walk test was observed in all subgroup diagnoses. There was no difference in the learning effect between disease severities. Conclusion: Both the 2- and 6-minute walk tests are associated with a learning effect. The learning effect is eliminated when correcting for heart rate in the 6-minute walk test, but not in the 2-minute walk test. The results suggest using a heart rate corrected 6-minute walk test to weed out day-to-day variations that are not due to a real change in the patient’s clinical condition.

Progressive fat replacement of muscle contributes to the disease mechanism of patients with single, large-scale deletions of mitochondrial DNA

Muscle dysfunction in mitochondrial myopathy is predominantly caused by insufficient generation of energy. We hypothesise that structural changes in muscles could also contribute to their pathophysiology. The aims of this study were to determine fat fractions and strength in selected muscles in patients with chronic progressive external ophthalmoplegia (CPEO), and compare progression of muscle fat fraction with age in individuals with CPEO vs. healthy controls and patients with the m.3243A>G mutation of mitochondrial DNA (mtDNA). Seventeen patients with CPEO and single large-scale deletions of mtDNA, 52 healthy controls, and 12 patients carrying the m.3243A>G mtDNA mutation were included. Muscle fat fractions were measured from cross-sections of paraspinal and leg muscles. Peak muscle strength was assessed from a static dynamometer. There was a direct correlation between age and fat fraction in all muscle groups in CPEO patients and healthy controls (p < 0.05). Analysis of covariance showed a higher progression rate of fat replacement in CPEO patients vs. healthy controls in studied muscle groups (p < 0.05). Patients with the m.3243A>G mutation had slower progression rates of fat replacement. Muscle strength decreased with increasing muscular fat fraction in CPEO patients, no correlation was seen in other groups. This indicates that structural muscle changes contribute to the phenotype of older patients affected by CPEO and large-scale deletions. It should therefore be considered, along with known energy deficiencies, as the cause of exercise intolerance.

Does grip strength reflect isokinetic muscle strength in lower limbs in patients with chronic inflammatory demyelinating polyneuropathy?: GS vs IKS in CIDP?

Introduction: Grip strength (GS) is a common measure of general muscle strength in patients with chronic inflammatory demyelinating polyneuropathy (CIDP). However, it is important to investigate the correlation and responsiveness of GS compared with isokinetic muscle strength (IKS) and function of the lower limbs. Methods: Seventy patients with CIDP were evaluated with GS, IKS, and functional measures of the lower limbs. Reevaluation was performed after 2 and 10/12 weeks. Correlation and response analyses were performed. Results: GS correlated with IKS at the ankle (IKSankle; maximum Spearmans rank‐order correlation [RS] = 0.58) and with walking performance (maximum RS = −0.38). IKSankle was more responsive to detect change (standardized response mean [SRM] = 0.57) than GS (SRM = 0.27). Discussion: GS does not seem to be an appropriate surrogate measure of IKS and function of the lower limbs in patients with CIDP. Muscle Nerve 58: 449–452, 2018

Aerobic anti‐gravity exercise in patients with Charcot–Marie–Tooth disease types 1A and X: A pilot study

Charcot–Marie–Tooth (CMT) disease is a hereditary neuropathy associated with impaired walking capacity. Some patients are too weak in the lower extremity muscles to walk at gravity with sufficient intensity or duration to gain benefit.