CLINICAL CASE | Loss of Vibration Sense and Limb Proprioception
A 36-year-old man was admitted to the hospital for unsteadiness of gait and several other somatic sensory and motor signs, including pain and limb strength impairments. Sensation to touch, pinprick, and temperature were normal. Perception of vibration and limb position sense were absent. When he was asked to stand upright with his eyes closed, he swayed and lost balance. His gait was broad based, clumsy, and staggering. MRI of his brain was normal but MRI of his spinal cord showed an intense signal in the dorsal columns, bilaterally (Figure 4–1A), that appeared to be the same as CSF. On interview, the patient told the resident that he had an untreated syphilitic infection for 10 or more years.
Try to answer the following questions based on your reading of the chapter, earlier readings, inspection of the case images, and consideration of the neurological signs.
1. What are the cellular constituents and processes in the dorsal column of a healthy individual?
2. What is the origin of the principal neural cells and cellular processes in the dorsal column?
3. What functional system becomes impaired when there is neuronal degeneration in the dorsal columns?
4. What distinguishes the spinal neural substrates of vibration sense and proprioception from pain, temperature, and itch. And why might touch sensation have been preserved?
5. What is Romberg’s sign and why does the patient demonstrate this sign?
Conclusion: The patient was diagnosed with neurosyphilis, also called tabes dorsalis, on the basis of neurological tests and several laboratory tests, including the MRI and the sensory modality loss. This is the advanced stage of syphilis, when it infects the nervous system. Key neurological signs and corresponding damaged brain structures Neurosyphilis
Syphilis is normally treated with penicillin. Left untreated, the infectious agent—the spirochete, Treponema pallidum—infects the nervous system. In time, this can result in dysfunction or degeneration of its neuronal targets. Common target neurons are the dorsal root ganglion sensory neurons, which are important for mechanosensation. Especially vulnerable is limb position sense (or limb proprioception), which is signaled by muscle and joint sensory receptors, and vibration sense, which is signaled by Pacinian corpuscles. At autopsy, tabetic patients can show degeneration of the dorsal columns, which is revealed by staining histological sections of the spinal cord for myelin. Oligodendrocytes also degenerate in regions where axons have degenerated, therefore showing demyelination (Figure 4–1B). The region of intense signal on the MRI demonstrates damaged dorsal column fibers. Loss of limb proprioception and vibration sense
Both of these senses are mediated by dorsal root ganglion neurons that have a large-diameter axon, which project rostrally within the dorsal columns. In the absence of limb proprioceptive afferents, patients rely on vision to compensate for the loss of sensory awareness of their limbs. This explains Romberg’s sign, the loss of balance when the patient closed his eyes. Touch is preserved in this patient; there ...