Contact heat evoked potentials reveal distinct patterns of spinal cord impairment in degenerative cervical myelopathy beyond MRI lesions

Abstract

Background: Magnetic resonance imaging may suggest spinal cord compression and structural lesions in degenerative cervical myelopathy (DCM) but cannot reveal functional impairments in spinal pathways. We aimed to assess the value of contact heat evoked potentials (CHEPs) in addition to MRI and hypothesized that abnormal CHEPs may be evident in DCM independent of MR-lesions and are related to dynamic mechanical cord stress. Methods: Individuals with DCM underwent neurologic examination including segmental sensory (pinprick, light touch) and motor testing. The presence or absence of hyperintense signal on T2-weighted MRI (T2-positive/negative) was assessed. Phase-contrast MRI was used to assess spinal cord motion as an indicator of dynamic mechanical stress. Dermatomal somatosensory evoked potentials and CHEPs were recorded after stimulation of dermatomes C6, C8, and T4 (CHEPs only) to assess spinal cord integrity. Results: Of 138 individuals included in this study (age 56 ± 13 years), 35% (N = 48) presented with T2-positive and 65% (N = 90) presented with T2-negative DCM. Abnormal CHEPs were present in T2-positive DCM (C6:41%; C8:32%; T4:24%) and T2-negative DCM (C6:35%; C8:54%; T4:26%). Multisegmental CHEP abnormalities at C6 and C8 were related to increased spinal cord motion (p = 0.030; ϵ2 = 0.072), and reduced upper extremity pinprick (p = 0.046; ϵ2 = 0.063) and motor scores (p = 0.005; ϵ2 = 0.108). Conclusions: CHEPs revealed distinct patterns of spinal cord impairment independent of structural T2-positive lesions, which were associated with measures of cord motion. CHEPs thus provide valuable complementary diagnostic insights into spinal cord integrity beyond MRI. This is especially important in incipient myelopathy to inform early diagnosis and timely interventions before the development of definite cord lesions.