CLINICAL CASE | Syringomyelia
Approximately one year earlier, a 41-year-old male sustained a painless burn to his right hand. The patient reported, at the time, that as the cigarette he was holding burned down, he noticed that his right index and middle fingers had sustained a burn, although he felt no pain. He reported that he noticed no other sensory, especially touch, or motor problems at that time. Over the next year, he began experiencing reduced right-hand grip strength in addition to the sensory loss. Then he sought medical care.
Neurological examination revealed an extensive territory, bilaterally, over the upper limbs and neck where there was minimal pain and thermal sensation (see Figure 5–1A). The analgesic region extended from the C5 to the T1 dermatomes. At this time, upper extremity tactile sensation and limb proprioception were now affected. Motor testing revealed denervation of several intrinsic right-hand muscles.
Figure 5–1A shows the classical distribution of pain and temperature loss in cervical syringomyelia. Figure 5–1B is an MRI showing a spinal cord syrinx, a pathological cavity coursing centrally and longitudinally within the central spinal cord. The syrinx produces the same MRI signal as CSF.
Answer the following questions based on your reading of the chapter, inspection of the images, and consideration of the neurological signs.
1. What are the key differences in the location of axons of the anterolateral system and dorsal column–medial lemniscal pathway that enabled the syrinx initially to interrupt pain but not touch or limb proprioception?
2. Why did the syrinx initially disrupt pain sensation but only later affect strength?
Key neurological signs and corresponding damaged brain structures Bilateral loss of pain and thermal senses Initially, the syrinx selectively damages the decussating anterolateral fibers producing the bilateral loss of pain and temperature senses; sparing touch and proprioceptive afferents in the dorsal columns. Figure 5–1C is a schematic illustrating the location of a typical syrinx in relation to decussating second-order axons of the anterolateral pathway. The central darkened region corresponds to the size of the syrinx when the patient first noticed pain loss, without additional neurological signs.
Bilateral loss of pain and thermal senses, together with loss of tactile and proprioceptive senses and hand weakness One year later, because of its enlarged size, the syrinx extends into the dorsal columns, thereby producing tactile and proprioceptive loss. Importantly, the syrinx is large enough also to damage motor neurons, producing hand weakness (Figure 5-1C; lighter region corresponds to the enlarged syrinx). Figure 5–1D is a histological section through the spinal cord of a person who had a syrinx at autopsy. The cavity would have been fluid-filled during life, showing more clearly the damage produced by the syrinx.