Development and validation of a rating scale for hereditary spastic paraplegia

Hereditary spastic paraplegia (HSP) is a clinically and genetically heterogeneous group of disorders characterized by slowly progressive lower extremity spasticity and weakness due to degeneration of the corticospinal tracts. Complicating symptoms of HSP include cognitive impairment, seizures, amyotrophy and peripheral neuropathy.

Little is known about the natural history of HSP and tools to measure severity of the disease are lacking. We aimed to develop and validate a HSP specific rating scale for clinical assessment of functional impairment caused by HSP. The rating scale was designed by a task force of the BMBF sponsored German Network of Hereditary Movement Disorders.

The HSP rating scale focuses on key features of pure HSP; additional „complicating“ symptoms are recorded in an inventory. The scale is composed of three parts:

A. Functional score including maximum walking distance, gait quality and speed, capacity to climb stairs and arise from a chair

B. Spasticity and weakness: evaluation following Ashworth scale and classification of the British Medical Research Council

C. Additional symptoms of pure HSP including contractures, pain, sensory deficits and bladder and bowel function

Every item is rated using a five point score. Maximum total score is 68 points.

In a first validation step 20 patients with HSP were investigated independently by the study coordinator (RS) as well as the local HSP specialist.

Overall interrater variability determined by intraclass correlation coefficient (ICC) was 0.84. ICC was >0.8 for all items of the functional score and was slightly less (>0.7) for spasticity and weakness items. Substantial variability was observed for rating of contractures (0.64) and sensory deficits (0.52).

Subscores and total score were correlated to landmarks of disability, a simple 4-point severity scale evaluating walking capacities. Good prognostic values were calculated for part A and C as well as the total score.

As an external plausibility test, we compared HSP ratings with the international co-operative ataxia rating scale (ICARS) and the minimental status examination (MMSE). We found good correlation between the HSP rating scale and ICARS (0.78) but poor correlation with MMSE (-0.15), supporting plausibility of the HSP rating scale.

In a revised version of the HSP rating scale rater instructions for the assessment of contractures have been modified and the item for sensory deficits has been removed. Final validation is currently conducted.