Neuroscience case 5 1. Speech comprehension, ability to speak, and word use were normal in Mr. Washburn, indicating that aphasia (cortical language problem) was not involved. However, he did have a problem with articulation, which is caused by impairment of the muscles or structures used to speak. This condition, known as dysarthria, can result from damage peripherally to the jaw, tongue, larynx or pharynx, or damage centrally to cranial nerve nuclei innervating those structures, the cerebellum, which coordinates those movements, or even the basal ganglia, which control the initiation of movement. In order to place all the symptoms in the context of a single lesion and have the symptoms regress over time, we need to locate a part of the nervous system where motor fibers that control the face, arm and leg are close together. Such an area is in the internal capsule where these fibers are adjacent and separated from the sensory, thalamocortical fibers traveling to the postcentral gyrus. If the UMN fibers are compressed or destroyed, lack of function will result. If they are merely compressed, not directly destroyed by ischemic necrosis, as the inflammatory process runs its course, the pressure will be gradually relieved, and their function may be recovered. This can happen if the major site of infarction is in the deep gray matter just adjacent to the internal capsule. Such lesions produce small cavities in the brain (less than 1 cm) known as lacunes. 2. He suffered a sudden occurrence of symptoms. Consciousness was not disturbed and there was no headache reported. This clinical presentation is typical of ischemia infarct or transient ischemic attack (TIA). This happens because of restriction of blood flow to a specific area of the brain. The restriction of blood flow is similar to that which happens in acute myocardial infarction and has the same pathogenic features. It can result from occlusion of a vessel (either by thrombosis or embolism), or marked narrowing due to atherosclerosis, upon which a superimposed episode of hypotension or hypoxemia further reduces the supply of oxygen to the distal tissue. If there is not adequate collateral circulation, the tissue will malfunction, and if the condition persists, the tissue will die (infarction). Hypertension is a major contributor to this process because of its influence on the development of atherosclerosis and particularly the narrowing of small vessels in the brain. The other risk factors are the same as those for myocardial infarction, i.e., smoking, high cholesterol, diabetes, family history, obesity, etc. 3. His falling to the left, left ataxia, and difficulty in left finger to nose movement all indicate a cerebellar problem, which could result from damage to cerebellum itself or structures/pathways that communicate with the cerebellum. The CSF data indicate that hemorrhage probably did not occur and that an infarct caused the symptoms. The differential diagnosis for these symptoms includes tumor, ischemia, hemorrhage, aneurysm, vascular malformation, abscess. 4. Explanation of symptoms: nystagmus vestibular nuclei or vestibulocerebellar components (ICP) LT ataxia LT cerebellum or related structure
decreased pain on LT face LT spinal trigeminal tract and nucleus decreased pain RT arm, trunk, leg LT ALS depressed LT corneal reflex LT spinal trigeminal tract and nucleus decreased gag reflex on LT hoarseness LT Nucleus ambiguus for CN IX, X difficulty swallowing ptosis/meiosis of LT eye hypothalamospinal fibers near ALS (Horner s syndrome) difficulty with finger to nose/heel to shin cerebellum, controls same side of body. The NIHSS score is 4 (considering 2 pts for the ataxia involving upper and lower limbs. 5. He has an acute lesion (infarct) in the left lateral medulla (see diagram). The symptom complex is called the Wallenberg Syndrome. Its various components are described in the accompanying table. The lesion is in the territory of the left posterior inferior cerebellar artery (PICA; see diagram). The corticospinal fibers are located ventromedially in the territory of the anterior spinal artery, which was not involved. His long-standing hypertension had produced narrowing and rigidity of his vessels, and the resistance to flow was abnormally high. The initial event was not as severe as a complete occlusion of PICA would produce, but when his blood pressure was abruptly and markedly lowered by medication, the perfusion pressure became too low to pass the stenotic segment, and a larger area became necrotic. This does not have to be a fatal lesion. Dr. Wallenberg s original patient lived six years after the episode, with a stable deficit, and died of an unrelated illness.
6. A) Patients in the study Part A = 291; Part B=333, B) Groups were well matched except for weight in Part 1 of the study and aspirin use and age in Part 2. The larger number of aspirin users in Part 2 may have biased the results toward a better outcome after tpa treatment compared to the placebo group. C) There was a benefit in tpa treatment for patients with ischemic stroke who were treated within 3 hr of the onset of symptoms. Compared with the placebo group, patients given tpa were 30% more likely to have minimal or no disability when assessed 3 months after therapy. TPA treatment did not increase significantly the rate of mortality although it did increase the frequency of hemorrhage. D) The NIHSS provided a quantitative method (based on a 42 pt scale) to assess the effects of treatment as well as a means to assess neurological deficits. The other tests were useful to assess other characteristics such as general disability and mortality. E) A 3 hr time limit was used to provide the best chance for recovery (minimize the effects of infarction) and to minimize the possibility of hemorrhage from thrombolytic therapy.
Structures Typically Affected in LATERAL MEDULLARY SYNDROME Nucleus ambiguus Diminished strength in the laryngeal and pharyngeal muscles on the same side of the throat as the lesion. Symptoms include hoarseness, difficulty swallowing, diminished gag reflex and a drooping palate on the side of the lesion with deviation of the uvula toward the unaffected (strong) side. Spinal trigeminal nucleus and tract At this level of the medulla, the spinal trigeminal tract carrying first order axons through the brainstem to the spinal trigeminal nucleus located at this and lower levels could be damaged. Damage to this structure and the portion of the spinal trigeminal nucleus located here can cause substantial loss of pain and temperature sensation from the same side of the face as the lesion. Anterolateral system Injury to the spinothalamic tract results in loss of pain and temperature sensation from extremities and trunk on the opposite side of the body from the lesion. Solitary nucleus Damage to this nucleus produces loss of taste sensation from the tongue on the same side as the lesion. The patient will complain of a diminished ability to taste food. (An unremarkable dinner perhaps?) Vestibular nuclei Damage to the vestibular nuclei can produce dizziness, vertigo and nystagmus. Inferior cerebellar peduncle The inferior cerebellar peduncle contains proprioception from the upper and lower extremity. Therefore, limb ataxia and intention tremor may be present in both upper and lower extremities on the same side as the lesion. Descending sympathetic tract axons from the hypothalamus Sympathetic motor neurons are located primarily in the thoracic spinal cord. Some of these sympathetic motor neurons innervate the face. They do so by leaving the spinal cord as preganglionic axons on thoracic spinal nerves. They
then synapse in the superior cervical ganglia. From there, post ganglionic axons travel with peripheral nerves and arteries to innervate the structures of the face. Axons of some hypothalamic neurons descend through the brainstem and cervical spinal cord and ultimately influence preganglionic sympathetic neurons in the upper thoracic spinal cord. If these descending hypothalamic axons are damaged on one side of the brainstem, sympathetic innervation to the face will be lost on the same side of the face. This results in a constellation of symptoms including ptosis (drooping of the eyelid from loss of sympathetic innervation to the smooth muscle component of the eyelid elevator), meiosis (chronic constriction of the pupil from loss of sympathetic innervation), an inability to sweat (anhidrosis) and a chronic flushing of the face all on the same side of the face as the lesion. All or some of the symptoms are possible with occlusion to the posterior inferior cerebellar artery. Collectively this constellation of symptoms is called Horner's syndrome.