Severity score system for progressive myelopathy: development and validation of a new clinical scale

Abstract

Progressive myelopathies can be secondary to inborn errors of metabolism (IEM) such as mucopolysaccharidosis, mucolipidosis, and adrenomyeloneuropathy. The available scale, Japanese Orthopaedic Association (JOA) score, was validated only for degenerative vertebral diseases. Our objective is to propose and validate a new scale addressing progressive myelopathies and to present validating data for JOA in these diseases. A new scale, Severity Score System for Progressive Myelopathy (SSPROM), covering motor disability, sphincter dysfunction, spasticity, and sensory losses. Inter- and intra-rater reliabilities were measured. External validation was tested by applying JOA, the Expanded Disability Status Scale (EDSS), the Barthel index, and the Osame Motor Disability Score. Thirty-eight patients, 17 with adrenomyeloneuropathy, 3 with mucopolysaccharidosis I, 3 with mucopolysaccharidosis IV, 2 with mucopolysaccharidosis VI, 2 with mucolipidosis, and 11 with human T-cell lymphotropic virus type-1 (HTLV-1)-associated myelopathy participated in the study. The mean ± SD SSPROM and JOA scores were 74.6 ± 11.4 and 12.4 ± 2.3, respectively. Construct validity for SSPROM (JOA: r = 0.84, P < 0.0001; EDSS: r = -0.83, P < 0.0001; Barthel: r = 0.56, P < 0.002; Osame: r = -0.94, P < 0.0001) and reliability (intra-rater: r = 0.83, P < 0.0001; inter-rater: r = 0.94, P < 0.0001) were demonstrated. The metric properties of JOA were similar to those found in SSPROM. Several clinimetric requirements were met for both SSPROM and JOA scales. Since SSPROM has a wider range, it should be useful for follow-up studies on IEM myelopathies.

Figure 1.. Distribution of the scores obtained in this study with the (I) SSPROM, (II) JOA, (III) Barthel, (IV) EDSS, and (V) Osame scales. Lower row: score distribution according to each disease under study. A = adrenomyeloneuropathy (AMN); B = mucopolysaccharidosis type I (MPS I), C = MPS type IV (MPS IV); D = MPS type VI (MPS VI); E = mucolipidosis (ML); F = human T-cell lymphotropic virus type-1-associated myelopathy (HTLV-1). SSPROM = Severity Score System for Progressive Myelopathy; JOA = Japanese Orthopaedic Association score; EDSS = Kurtzke Expanded Disability Status Scale; OSAME = Osame Motor Disability Score.

Figure 2.. Distribution of (A) age at onset, (B) SSPROM and (C) JOA scores according to the different diseases under study. Data are reported as the mean, SD, and range. SSPROM = Severity Score System for Progressive Myelopathy; JOA = Japanese Orthopaedic Association score; AMN = adrenomyeloneuropathy; MPS = mucopolysaccharidosis types I, IV and VI; ML = mucolipidosis; HTLV-1 = human T-cell lymphotropic virus type-1.

Figure 3.. Correlations between SSPROM and other scales under study. SSPROM = Severity Score System for Progressive Myelopathy; JOA = Japanese Orthopaedic Association score; EDSS = Kurtzke Expanded Disability Status Scale; OSAME = Osame Motor Disability Score.

Figure 4.. Correlations between disease duration and SSPROM in (A) HTLV-1 infection and (B) adrenomyeloneuropathy, and between (C) disease duration and JOA for adrenomyeloneuropathy. SSPROM = Severity Score System for Progressive Myelopathy; JOA = Japanese Orthopaedic Association score; AMN = adrenomyeloneuropathy; HTLV-1 = human T cell lymphotropic virus type-1.