Normal proprioceptive trigeminal afferents in patients with Sjogren's syndrome and sensory neuronopathy. A pure sensory neuropathy due to neuronal damage in the gasserian and spinal ganglia has been described in patients with Sjogren's syndrome. Conventional electromyographic (EMG) studies can demonstrate the selective involvement of the sensory pathways but they do not provide definite evidence for the site of the lesion. Noting that the trigeminal sensory neurons carrying cutaneous and muscular afferents are differentially located in the gasserian and mesencephalic nuclei, respectively, we carried out an electrophysiological study of the trigeminofacial and trigeminotrigeminal reflexes in 5 patients with Sjogren's syndrome and pure sensory neuropathy, in 10 patients with sensory-motor neuropathies of other causes, and in 10 healthy subjects. Our results show that patients with Sjogren's syndrome and pure sensory neuropathy who exhibited abnormal blink reflexes and an abnormal, cutaneous-induced masseter silent period had normal jaw jerks, whereas patients with sensory-motor neuropathies who exhibited abnormal cutaneous responses had abnormal jaw jerks. These findings suggest that the lesion in pure sensory neuropathy involves damage to the neurons of the gasserian ganglia and not to the trigeminal axons, since an axonal lesion would be expected to involve the large axons from muscle spindle receptors. 