Neuronopathy in the dorsal root ganglia, accompanied by the loss of peripheral sensory nerve fibers and the degeneration of posterior columns of the spinal cord, is a hallmark Friedreich's ataxia. Progressive loss of alpha-motor neurons in the anterior horn of spinal cord is characteristic of spinal muscular atrophy, not Friedreich's ataxia.
Friedreich's ataxia is an autosomal recessive condition characterized by spinocerebellar degeneration. Prevalence is 1 in 50,000. An ataxic gait is usually the presenting symptom with onset between 7 and 15 years of age. The clinical triad for diagnosis is ataxia, areflexia, and a positive Babinski reflex. The disease is progressive, and almost all patients are wheelchair bound by the first or second decade of life. They usually die in the fourth or fifth decade as a result of cardiomyopathy, pneumonia, and aspiration. Friedreich's ataxia is characterized by degeneration of posterior columns of the spinal cord.
The primary concern for the orthopaedist is the correction of foot and spinal deformities. In patients with Friedreich's ataxia, the plantar reflex is sometimes so powerful that when standing is attempted, the feet and toes immediately plantarflex and the tibialis posterior tendon pulls the forefoot into equinovarus. Early on tenotomies and bracing should be done, but once the cavovarus deformity is rigid, then a triple arthrodesis is recommended to provide a solid base of support for a fixed plantigrade foot.
Scoliosis is commonly found in Friedreich's ataxia. Scoliosis will usually progress if the onset of disease is before 10 years of age and scoliosis develops before age 15. The treatment recommendation is to observe curves less than 40 degrees, operate on those greater than 60 degrees, with a gray area between 40 and 60 degrees. A single stage posterior arthrodesis with segmental instrumentation is the treatment of choice from the upper thoracic to the lower lumbar spine.
Pandolfo et reviews the genetics and pathophysiology of Friedreich's ataxia. They report it is caused by hyperexpansion of GAA repeats in the first intron of the frataxin gene. Variation in neurophysiological abnormalities is correlated with the size of the GAA repeat expansion and likely accounts for individual variation in the progression of FRDA.
Orthopaedic Knowledge Update 8: Home study syllabus, Edited by Alexander R. Vaccaro, MD
Pandolfo M. Friedreich ataxia: the clinical picture. J Neurol. 2009 Mar;256 Suppl 1:3-8. Review
PMID:19283344 (Link to Abstract)