Dissociative sensory loss occurs in

Syringomyelia: A long cavity (the syrinx) filled with CSF develops within the spinal cord, most commonly in the cervical region. Usually the cause is unknown but the condition is sometimes associated with prolapse of the cerebellar tonsils and hydrocephalus The expanding cyst presses on the anterior horn cells, producing weakness and wasting of the hand muscles. Destruction of the decussating spinothalamic fibers in the center of the cord produces a characteristic dissociated sensory loss in the upper limbs - impaired response to pain and temperature but preservation of touch.(light touch along with vibration and position is transmitted through posterior column) CT may reveal an expanded cord and the syrinx can be defined on MRI. Deterioration may be slowed down by decompression of the foramen magnum. Tuberculosis of spine: Predominantly motor involvement. Disc Prolapse: In the lumbar region it commonly affects the nerve roots thus involving all five sensory modalities. Tabes dorsalis(teiary syphillis): Involvement of posterior column thus involving light touch, proprioception and vibration.