Physiological functions of the ascending spinal tracts in HTLV-I-associated myelopathy (HAM). 
Physiological functions of the spinothalamic tract (STT) and the posterior column (PC) were studied in 19 Japanese patients with HTLV-I-associated myelopathy (HAM).  The former was evaluated by pain-related somatosensory evoked potentials (SEPs) following CO2 laser stimulation, and the latter by conventional SEPs following electrical stimulation.  Conduction velocity of STT and PC was significantly decreased in 9 and 14 patients, respectively, and more than half of them showed no clinical impairment of sensations (subclinical abnormality).