Hereditary Spastic Paraplegia: Beyond Clinical Phenotypes toward a Unified Pattern of Central Nervous System Damage

Abstract

Purpose: To investigate whether specific patterns of brain gray matter (GM) regional volumes and white matter (WM) microstructural abnormalities and spinal cord atrophy occur in patients with pure and complicated hereditary spastic paraplegias (HSPs). Relationships between clinical and cognitive features of patients with HSP who had brain and cervical cord damage were also investigated.

Materials and methods: This study was approved by the local ethical committees on human studies, and written informed consent from all subjects was obtained prior to enrollment. Forty-four patients with HSP (20 genetically defined cases and 24 without genetic diagnosis) and 19 healthy control subjects underwent clinical, neuropsychological, and advanced magnetic resonance (MR) imaging evaluations. Patterns of GM atrophy and WM microstructural damage obtained by using structural and diffusion-tensor MR imaging were compared between groups. Cervical cord atrophy was also assessed by using an active surface method. Correlations between clinical, cognitive, and diffusion-tensor MR imaging measures were evaluated.

Results: Clinical data showed that spastic paraplegia is accompanied by a number of other features, including sensory disturbances, and verbal and spatial memory deficits, not only in complicated HSP but also in pure HSP. MR imaging demonstrated a similar involvement of motor, association, and cerebellar WM pathways (P < .05, family-wise error corrected for multiple comparisons) and cervical cord (P < .001) in patients with HSP relative to healthy control subjects, regardless of their clinical picture. The severity of WM damage correlated with the degree of spasticity (P < .05, family-wise error corrected) and cognitive impairment (r values, -0.39 to 0.51; P values, .001-.05) in both pure and complicated HSP.

Conclusion: The detection of a distributed pattern of central nervous system damage in patients with pure and complicated HSP suggests that the "primary" corticospinal tract involvement known to occur in these patients may be associated with a neurodegenerative process, which spreads out to extramotor regions, likely via anatomic connections. This observation is in line with emerging pieces of evidence that, independent of the clinical phenotype, there is a common neurodegenerative cascade shared by different neurologic disorders.