Leg pain is related to back pain in 25-65% of all cases and classified as somatic referred pain or radicular pain. However, distinction between the two may be challenging as different pathomechanisms may cause similar patterns of pain. For this reason a pathomechanism based classification system was proposed, with four distinct hierarchical and mutually exclusive categories: Neuropathic Sensitization (NS) comprising major features of neuropathic pain with sensory sensitization; Denervation (D) arising from significant axonal compromise; Peripheral Nerve Sensitization (PNS) with marked nerve trunk mechanosensitivity; and Musculoskeletal (M) with pain referred from musculoskeletal structures. The objective of this study was to examine construct validity of the classification system. Construct validity was investigated by determining the relationship of nerve functioning with subgroups of patients and asymptomatic controls. Thus somatosensory profiles of subgroups of patients with low back related leg pain (LBRLP) and healthy controls were determined by a comprehensive quantitative sensory test (QST) protocol. It was hypothesized that subgroups of patients and healthy controls would show differences in QST profiles relating to underlying pathomechanisms. 77 subjects with LBRLP were recruited and classified in one of the four groups. In addition, 18 age and gender matched asymptomatic controls were measured. QST revealed signs of pain hypersensitivity in group NS and sensory deficits in group D whereas Groups PNS and M displayed no significant differences in comparison to the asymptomatic group.
The findings of this study support construct validity for two of the categories of the new classification system, although further research is called for to achieve construct validation of the classification system as a whole.