Clarifications of the Motor Level Definition in the International Standards for Neurological Classification of Spinal Cord Injury in Not Clinically Testable Myotomes.

Background: In the International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI), two approaches for determining motor levels (MLs) in not clinically testable myotomes (C2-C4, T2-L1, S2-S5) are described: one where the motor level follows the sensory level (MFSL) and another deriving motor function from sensory function (MFSF). Their results differ when (1) all key muscles of an upper (or upper and lower) extremity are scored as intact, (2) sensation is not normal in key muscle segments, and (3) a contiguous region of normal sensation starts at T2 (or S2).

Objectives: This work aims to characterize these cases and to discuss explanations.

Methods: We analyzed 1330 early and late ISNCSCI assessments of 665 individuals from EMSCI.

Results: Forty-nine (3.6% of all 2660 MLs) MFSL (63.3% T1, 36.7% S1) and MFSF MLs from 34 individuals differed without consequences on ASIA Impairment Scale (AIS) grades (4 AIS A, 1 AIS B, 29 AIS D). In 16 AIS D cases, all testable motor functions were intact, with a mean Spinal Cord Independence Measure (SCIM) total score of 95.67 ± 3.51 in 3 individuals with MFSL-ML T1 and 100 in 5 individuals with MFSL-ML S1. The MFSF-MLs are on average 9.63 ± 7.50 (T1: 12.16 ± 8.43; S1: 5.28 ± 1.36) segments caudal to the sensory level (SL).

Conclusion: We identified and characterized rare cases with an unusual sensory impairment pattern, which could be explained by an isolated damage of afferent spinal tracts or the presence of non-SCI conditions. Further investigations of these case are necessary for a more conclusive ML definition.