Natural history of muscle weakness in Friedreich's Ataxia and its relation to loss of ambulation.

From 1979 to 1992, 170 muscular assessments performed on 33 patients with Friedreich's Ataxia were reviewed. The average followup was 6 years. All muscle evaluations were done by the same team. It was possible to delineate a fairly regular and statistically significant pattern of slowly progressive and symmetrical loss of strength affecting mainly the lower limbs, and more specifically the pelvic girdle muscles. The first significant weakness was observed in the hip extensor group, followed in a variable fashion by other muscle groups of the lower limb. Upper limb and trunk muscles remained relatively spared until late in the disease process, with an overall strength approximately 80% of normal. Use of a wheelchair began at a mean age of 18.2 years, at which time the lower-limb strength averaged 70% of normal. Patients became totally unable to walk at a mean of age 20.5 years old, with a further decline in lower limb strength to 56% of normal. Weakness does not appear to be the primary cause for loss of ambulation in patients with Friedreich's ataxia.