✓ In 12 cats and two Macaca mulatta monkeys, areas of chronic focal injury were induced in the trigeminal root by implantation of a chromic suture in the nerve near its entry into the brain stem. Experimental lesions were examined histologically and electrophysiologically at 1 week, 3 weeks, and 6 weeks after surgery. At 3 weeks following implantation, lesioned nerves showed areas of focal inflammation surrounding implanted sutures with prominent demyelination of adjacent axons. A total of 497 trigeminal units were studied, 304 of which had associated demyelination of the root. In these 304 cells, two types of abnormal impulse generation from areas of focal demyelination were recorded. Reflected orthodromic action potentials and prolonged high-frequency after-discharges following short priming trains of orthodromic stimuli were observed in 23% and 4% of cells, respectively. Ectopic spike initiation from areas of focal demyelination was not dependent upon anatomical continuity of the nerve with the brain stem, was augmented by hyperventilation, and could be eliminated by the intravenous administration of diphenylhydantoin sodium. The relevance of these findings to the pathophysiological mechanisms of pain syndromes involving peripheral nerves in general and the trigeminal system in particular is discussed.
The Wada Test
Kim J. Burchiel
Kim J. Burchiel
✓ Sixty patients with trigeminal neuralgia or atypical facial pain were followed for an average of 1 year after percutaneous retrogasserian glycerol rhizolysis. The procedure was initially effective in relieving pain in 80% of the patients with typical trigeminal neuralgia and symptomatic trigeminal neuralgia secondary to multiple sclerosis. However, life-table analysis indicated that 50% of this group had persistence or recurrence of pain within 18 months after the operation. Percutaneous retrogasserian glycerol rhizolysis was ineffective in relieving atypical trigeminal neuralgia or atypical facial pain. Minor complications occurred in 23% of patients, and major morbidity was seen in 1.6%. Facial sensory loss which persisted for more than 1 month was found in 72% of patients, corneal hypesthesia occurred in 15%, and an additional 7% had corneal anesthesia. The data indicate that the success of percutaneous retrogasserian glycerol rhizolysis in relieving trigeminal neuralgia is directly related to the production of facial sensory loss.
Terrence L. Pencek and Kim J. Burchiel
✓ Although it is well documented that retained foreign bodies are associated with delayed intracranial abscess, there are few reports of anaerobic organism growth. A case is presented in which a left parieto-occipital abscess surrounded a metallic fragment implanted when a mortar shell exploded in Vietnam 15 years before. The diagnostic evaluation and surgical management of this case are presented.
Kim J. Burchiel and Lisa C. Russell
✓ Thirty-five Sprague-Dawley rats with saphenous neuromas underwent acute microfilament recording in the proximal nerve. The effect of the potassium channel-blocking agents, tetraethylammonium bromide (TEA) and 4-aminopyridine, on spontaneous activity in A fibers terminating in the neuroma was observed. The effects of gallamine were also tested. Of the two channel-blocking agents, TEA reliably increased spontaneous firing in active fibers and initiated spontaneous activity in some fibers with no spontaneous baseline discharge. 4-Aminopyridine had no effect on baseline activity of either spontaneously active or quiescent fibers; however, it inhibited spontaneous activity induced by prior TEA treatment. Gallamine application produced effects similar to TEA in that spontaneous activity was dramatically increased. These results imply that a tonic potassium conductance is present in regenerating fibers in the neuroma and that this conductance moderates the tendency toward hyperexcitability and spontaneous firing. Spontanous activity in nociceptive afferent fibers may represent the mechanism of chronic pain and paresthesias that often accompany peripheral nerve injury. These results suggest that agents which either increase potassium conductance or selectively inhibit the sodium current in regenerating axons might be effective in the treatment of these chronic pain syndromes.
Kim J. Burchiel and Lisa C. Russell
✓ The effect of topical glycerol application on normal and previously injured saphenous nerves was tested in 20 Sprague-Dawley rats. Anhydrous glycerol treatment of five normal nerves showed a rapid loss of C-fiber conduction within 5 minutes of application, while after 10 to 30 minutes, a complete conduction blockade in all fiber types was produced. The effect of anhydrous glycerol on both spontaneous firing from the neuroma and impulse propagation within the nerve was examined in 11 rats that had undergone saphenous neurotomy 7 days previously. In these animals, cessation of spontaneous action potential production from the neuroma was the earliest electrophysiological change noted, followed by loss first of C-fiber, then of A-fiber conduction. Graded concentrations of glycerol (25%, 50%, 75%, and 100%) were used in four rats with saphenous neuromas, which allowed selective blockade of spontaneous action potential generation and C-fiber conduction with minimal effect on A-fibers.
The neurophysiological mechanism of glycerol neurolysis appears to be a nonspecific conduction blockade of large and small fibers, which is established within minutes of its application. Spontaneous firing within damaged axons, which may play a role in a variety of cranial and peripheral nerve sensorimotor syndromes, is also exquisitely sensitive to glycerol application.
Kim J. Burchiel and Thomas K. Baumann
✓ The origin of trigeminal neuralgia (TN) appears to be vascular compression of the trigeminal nerve at the root entry zone; however, the physiological mechanism of this disorder remains uncertain. The authors obtained intraoperative microneurographic recordings from trigeminal ganglion neurons in a patient with TN immediately before percutaneous radiofrequency-induced gangliolysis. Their findings are consistent with the idea that the pain of TN is generated, at least in part, by an abnormal discharge within the peripheral nervous system.
Kim J. Burchiel and Gottfried Schmer
✓ A rapid fluorometric assay technique has been utilized to assess the degree of fibrinolytic inhibition in 20 patients with ruptured intracranial aneurysms treated with epsilon-aminocaproic acid (EACA). This method quantitates the available plasminogen activity (APA) of plasma, and has proven to be a reliable means of monitoring antifibrinolytic therapy. Determination of the plasma APA also permits correlation of the level of fibrinolytic activity with putative complications of EACA therapy. Normal control plasma APA was 3.1 ± 0.7 CTA units/ml, but in patients with subarachnoid hemorrhage (SAH), pretreatment fibrinolytic activity was supranormal at 3.78 ± 0.88 CTA units/ml. During continuous intravenous administration of EACA (1.5 gm/hr) in patients with SAH, the plasma fibrinolytic activity was decreased to 0.9 ± 0.31 CTA units/ml. A case is described which exemplifies the use of this assay. In addition, an approach to monitoring antifibrinolytic therapy using the plasma APA is proposed.
Kim J. Burchiel and Lisa C. Russell
✓ In 18 Sprague-Dawley rats, the left sciatic nerve was divided at the mid-femur level. Seven to 9 days later, microfilament recordings were made from the ipsilateral L-5 ventral root. Spontaneous activity in the ventral root, ranging from 0.1 to 6.1 Hz, was recorded in 12 of the 18 animals. Conduction velocity determinations showed this activity to be in A-beta and A-delta fibers. Recordings in 10 normal L-5 ventral roots from five control rats showed no spontaneous activity. In the rats with sciatic nerve division, the ongoing discharge appeared to originate in the cut end of the nerve since mechanical stimulation of the neuroma produced synchronous ventral root activity. Furthermore, cooling of the neuroma inhibited the spontaneous discharge, whereas with rewarming it returned. Spontaneous ventral root activity was also increased by systemic application of epinephrine. This activity was qualitatively similar to spontaneous activity that has been recorded in dorsal root microfilaments after peripheral nerve injury. The observation of an ongoing discharge in potentially nociceptive ventral root axons subsequent to nerve injury may be relevant to the mechanism of chronic pain of peripheral origin.