Pearls and pitfalls: Electrophysiology for primary headaches

Background Primary headaches are functional neurological diseases characterized by a dynamic cyclic pattern over time (ictal/pre-/interictal). Electrophysiological recordings can non-invasively assess the activity of an underlying nervous structure or measure its response to various stimuli, and are therefore particularly appropriate for the study of primary headaches. Their interest, however, is chiefly pathophysiological, as interindividual, and to some extent intraindividual, variations preclude their use as diagnostic tools. Aim of the work This article will review the most important findings of electrophysiological studies in primary headache pathophysiology, especially migraine on which numerous studies have been published. Results In migraine, the most reproducible hallmark is the interictal lack of neuronal habituation to the repetition of various types of sensory stimulations. The mechanism subtending this phenomenon remains uncertain, but it could be the consequence of a thalamocortical dysrythmia that results in a reduced cortical preactivation level. In tension-type headache as well as in cluster headache, there seems to be an impairment of central pain-controlling mechanisms but the studies are scarce and their outcomes are contradictory. The discrepancies between studies might be as a result of methodological differences as well as patients’ dissimilarities, which are also discussed. Conclusions and perspectives Electrophysiology is complementary to functional neuroimaging and will undoubtedly remain an important tool in headache research. One of its upcoming applications is to help select neurostimulation techniques and protocols that correct best the functional abnormalities detectable in certain headache disorders.

Pathological effects and motor response threshold changes following radiofrequency application at various distances from the L-5 nerve root: an experimental study

Object Radiofrequency (RF) ablation is a minimally invasive technique often used percutaneously in the treatment of many conditions such as spasticity, pain, and osteoid osteoma. The purpose of this study was to assess the value of motor response threshold (MRT) as an indirect indicator of the RF generator's electrode to nerve distance, and to evaluate the effects of RF at various distances from a nervous structure. Methods The L-5 nerve root was studied in 102 Sprague-Dawley rats (sham contralateral side). Motor response thresholds at 0, 2, 4, 5, and 6 mm from the nerve root were assessed before and after RF application for 2 minutes at 80° C on Days 0 and 7. Radiofrequency was applied 0, 2, 4, 5, and 6 mm away from L-5 and with the addition of interposed cortical bone. The effects of RF application on MRT were studied, and subsequent nerve injury was evaluated using light microscopy pathological examination. Results There is a significant correlation between MRT and the distance between the electrode tip and L-5, with MRT less than 0.5 V when the electrode was in direct contact with the root. Electrical and pathological changes following RF application were more pronounced at 0 mm, with worsening seen on Day 7. Radiofrequency at 2 and 4 mm produced fewer electrical and histological deleterious effects on the nerve on Days 0 and 7, with an obvious improvement on Day 7. At 5 mm, electrical and histological abnormalities were minimal on Day 0 and were fully reversible on Day 7. At 6 mm and with interposed cortical bone, MRT and pathological findings were unchanged on Days 0 and 7. Conclusions The MRT proved to be a useful and reliable tool in decreasing nerve morbidity following RF ablation in animals and may be used in humans for the same purpose. It serves as an indirect indicator of the proximity of the RF generator's electrode tip to any adjacent motor nervous structure. A minimum safe distance of 5 mm between the electrode tip and the nerve is required to avoid irreversible nerve injury, unless a bony wall is interposed between them, thus serving as a nerve shield. In medical conditions that require RF ablation of the nerve, such as spasticity and pain, the MRT must be lower than 0.5 V. When a nerve lesion is to be avoided such as in cases of osteoid osteoma, an MRT higher than 2.5 V is considered safe, reflecting a distance greater than 5 mm.

The shaping of animals’ minds

Mind is seen as a collection of abilities to take decisions in biologically relevant situations. Mind shaping means to form habits and decision rules of how to proceed in a given situation. Problem-specific decision rules constitute a modular mind; adaptive mind-shaping is likely to be module-specific. We present examples from different behaviour ‘faculties’ throughout the animal kingdom, grouped according to important mind-shaping factors to illustrate three basically different mind-shaping processes: (I) external stimuli guide the differentiation of a nervous structure that controls a given behaviour; (II) information comes in to direct a fixed behaviour pattern to its biological goal, or to complete an inherited behaviour program; (III) specific stimuli activate or inactivate a pre-programmed behaviour. Mind-shaping phenomena found in the animal kingdom are suggested as ‘null-hypotheses’ when looking at how human minds might be shaped.

Re-evaluation of the distributions of dystrophin and utrophin in sciatic nerve

Differential expression of proteins belonging to the dystrophin family was analysed in peripheral nerves. In agreement with previous reports, no full-size dystrophin was detectable, only Dp116, one of the short dystrophin products of the Duchenne muscular dystrophy (DMD) gene. We used specific monoclonal antibodies to fully investigate the presence of utrophin, a dystrophin homologue encoded by a gene located on chromosome 6q24. Evidence is presented here of the presence of two potential isoforms of full-length utrophin in different nerve structures, which may differ by alternative splicing of the 3′-terminal part of the utrophin gene according to the specificities of the monoclonal antiobodies used. One full-length utrophin was co-localized with Dp116 in the sheath around each separate Schwann cell-axon unit, but the other utrophin isoform was found to be perineurium-specific. We also highlighted a potential 80 kDa utrophin-related protein. The utrophin distribution in peripheral nerves was re-evaluated and utrophin isoforms were detected at the protein level. This preliminary indication will require more concrete molecular evidence to confirm the presence of these two utrophin isoforms as well as the potential 80 kDa utrophin isoform, but the results strongly suggest that each isoform must have a specialized role and function within each specific nervous structure.

Pelvic lymphadenectomy: Anatomic considerations

The real significance of pelvic lymphadenectomy, cure or staging, is still unknown. The morbility of this procedure is surely proportional to the extension of lymph node ablation. Bleeding, intraoperative lesions of nervous structure (lumbo-sacral trunk) post-operative lymphocele, but also lesion of the inferior hypogastric plexus and pelvic branches are more frequent in the case of extended (all the hypogastric and pre-sacral lymph nodes) than limited procedures. Therefore pelvic lymphadenectomy in the case of urologic malignancy is obviously incomplete. Nevertheless the incidence of recurrences in the remaining lymphatic structure is neither high nor clinically significant an therefore the indication for limited procedures is reinforced.

Exploration of selected brachial plexus lesions by the posterior subscapular approach

✓ The application of an old surgical technique, previously employed for treatment of thoracic outlet syndromes, to lesions of the brachial plexus is discussed. Positioning of the patient, the surgical procedure, and selected indications for a posterior subscapular approach with resection of the first rib are discussed. The indications for the use of this approach are: proximal plexus lesions involving roots and/or trunks believed to be repairable, complicated thoracic outlet syndromes, prior anterior exploration for vascular or nervous structure disease, and progressive plexus palsy associated with damage to the soft tissue of the anterior chest wall and supraclavicular regions secondary to irradiation. The authors' experience to date with 12 such cases is presented in chart form, while five cases are presented in some detail.