Dermatomal somatosensory evoked potentials in the diagnosis of lumbosacral radiculopathies.

The diagnostic sensitivity of dermatomal somatosensory evoked potentials (DSEPs) was evaluated in a homogeneous group of fifteen patients with low back pain due to isolated lumbosacral radiculopathy. The normative values from L3 to S1 were defined, as were the parameters of abnormality. In seven patients with pseudoradicular or referred leg pain, a negative neurological examination and images indicative of protrusion or paramedian disc hernia, the DSEPs were normal in six cases and slightly altered in one. In eight patients with deafferentation leg pain, clinical signs of root damage and images indicative of an intraforaminal hernia, the DSEPs showed varying degrees of alteration which could generally be correlated to the severity of the clinical picture. This method can therefore be useful in differentiating pain due to stimulation of the receptors of the osteoarticular structures or the root sheath, in which the DSEPs are normal, from pain due to direct root damage, in which the DSEPs are altered. This functional evaluation of anatomical damage provides further information which may help to achieve a better therapeutic approach.