Hereditary spastic paraplegia (HSP) is a genetically heterogeneous group of neurodegenerative disorders characterized by progressive lower extremity weakness and spasticity. HSP pathology involves axonal degeneration that is most pronounced in the terminal segments of the longest descending (pyramidal) and ascending (dorsal columns) tracts. In this study, we compared spinal cord magnetic resonance imaging (MRI) in 13 HSP patients with four different types of autosomal dominant hereditary spastic paraplegia (SPG3A, SPG4, SPG6, and SPG8) with age-matched control subjects. The cross-section area of HSP subjects at cervical level C2 was 59.42±12.57 mm 2 and at thoracic level T9 was 28.58±5.25 mm 2 . Both of these values were less than in the healthy controls ( p <0.001). The degree of cord atrophy was more prominent in patients with SPG6 and SPG8 who had signs of severe cord atrophy (47.60±6.58 mm 2 at C2, 21.40±2.4 mm 2 at T9) than in subjects with SPG3 and SPG4 (66.0±8.94 mm 2 at C2, p <0.02; 31.75±2.76 mm 2 at T9, p <0.001). These observations indicate that spinal cord atrophy is a common finding in the four genetic types of HSP. Spinal cord atrophy was more severe in SPG6 and SPG8 HSP subjects than in other types of HSP we studied. This may suggest a different disease mechanism with more prominent axonal degeneration in these two types of HSP when compared with HSP due to spastin and atlastin mutations
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