Funded By:
By W.M. Fowler, Jr., MD, G.T. Carter, MD, D.D. Kilmer,
MD, E.R. Johnson, MD,
S. Aitkens, N. Wright, and T. Abresch, MS.
RTC/Neuromuscular Diseases, Department of PM&R, Univ. of Calif., Davis, and National Institute on Disability and Rehabilitation Research.
The hereditary neuropathies include hereditary motor sensory neuropathy (HMSN), hereditary motor neuropathy and hereditary sensory and autonomic neuropathy, and each group includes several types. HMSN, with at least eight types, is one of the most common neuromuscular diseases. HMSN, types I and II, are usually considered to represent the Charcot-Marie-Tooth syndrome. While the characteristics of HMSN are well known, description of these characteristics has been primarily based on clinical observations, and there have not been any studies using specific measurements to evaluate each characteristic of the disease in terms of a natural history profile. In addition, there have been few, if any, investigations of the incidence and description of some of the characteristics such as contractures, spinal deformity, pulmonary and cardiac function, mental, intellectual and cognitive function, and psychosocial adjustment.
The purpose of this study was to develop a comprehensive impairment and disability profile for HMSN. Impairment was evaluated by measurements of strength, contractures, spine deformity, cardiac function, pulmonary function and intellectual capacity. Impairment frequently leads to disability. Disability evaluations consisted of measures of mobility and upper extremity function, cardiopulmonary adaptations, cardiac and pulmonary disease, and psychosocial adjustment.
One hundred and twenty patients followed in a regional Neuromuscular Disease (NMD) Clinic, 1982-1992, were reviewed. Sixty-eight were males and fifty-two were females. Age was 44 ± 18 years and disease duration 33 ± 14 years at the time of the first clinic visit. Six percent were non-ambulatory, and age at loss of ambulation was 29 ± 14 years. Only two were known to have died during the ten year period. All participants from the clinic did not receive all measurements so the individuals in each of the impairment or disability profiles would be considered as samples of the larger clinic population.
When appropriate, results from the individuals with HMSN were compared with able bodied control subjects and/or established reference standards. In addition, the effect of age and disease duration was evaluated by both one time event (cross sectional) and longitudinal analysis. In the former, the first measurement obtained on every subject was plotted against years of age and disease duration. In the latter, each measurement for each individual for a three or more years period of time was analyzed for any age or disease duration effect.
Body Composition and Metabolism: Anthropometric and body composition measurements were obtained in a sample of 51 individuals from the clinic population. Anthropometric measures of height, bisacromial and biilliac diameters, wrist and ankle circumferences, and chest depth were within normal limits in the HMSN group when compared to gender and age matched control able-bodied subjects and reference standards. Although body weight was slightly higher (13%) when compared to control, it was within normal limits when compared to reference standards. There was no significant age or disease duration effect in the adult individuals.
Circumferential diameters of the arm, thigh, forearm and calf were not significantly different between the HMSN and control groups. However, while circumferences increased with age in the control subjects, there were not any changes with age or disease duration in the HMSN group indicating that muscle atrophy (wasting) occurred but was very slowly progressive.
The sum of five skinfold thickness measurements (triceps, subscapular, thigh, abdomen, suprailiac) was 30% higher in the HMSN group when compared to controls. Females in both groups had 25% to 35% greater skinfold thickness measurements than males. Thickness increased with age in both groups, but increased with age and disease duration to a greater extent in males with HMSN. Predicted percent fat, derived from skinfold thickness measurements, was 22% higher in the HMSN group indicating higher subcutaneous fat stores. As with skinfold thickness, females in both groups had a higher percent predicted fat than males with a similar age and disease duration pattern. Since muscle wasting was relatively mild and slowly progressive, there was no significant difference between HMSN and controls in lean weight and resting metabolic rate.
Muscle Weakness Profile: Muscle strength was evaluated by both manual muscle testing (MMT) and quantitative measurements.
MMT: MMTs were obtained in a sample of 53 individuals from the clinic population. Grading was on a 0-5 scale, in which 5 is normal, for 34 muscle groups. The total strength grade for all muscle groups combined was 3.9 0.7 MMT units (complete range of motion against gravity plus minimal resistance from the therapist). In cross-sectional one-time event analysis of the 53 individuals, there was a slight but significant decline in total strength of -0.015 MMT units/year of disease duration.
Average grades for clusters of muscle groups showed that the lower extremity muscles were significantly weaker than the upper extremity muscles, the distal muscle weaker than the proximal muscles, and no difference in strength between flexor and extensor muscle groups. In general, the rate of strength decline was more rapid in the weaker muscle groups in the lower extremities.
