Quantitative sensory testing

The diagnosis and treatment of peripheral neuropathy from any cause has come to the forefront of the research community in the past few years. Both past and new diagnostic and treatment options have been and are being studied to better understand and properly treat this debilitating and sometimes devastating disease.One such advancement is the clinical use of quantitative sensory testing. To identify etiology of the neuropathy early, the testing instrument would need to identify changes throughout the course of the disease, have a normative database, and show a clear distinction between the absence or presence of disease. The pressure specified sensory device (PSSD) was developed in 1992 to painlessly investigate the cutaneous pressure thresholds quantitatively and accurately.     

Deltoid sensory flap

Eight patients were treated using the deltoid sensory flap for soft-tissue injury of the extremities. The results were one-stage reconstructions of soft tissue extremity injuries. Protective sensibility was provided to the reconstructed area; there was no limitation of motion of the shoulder after the procedure; and primary closure of the donor site was feasible. The advantages of the deltoid sensory flap exceed those of other reconstructive procedures that are used in areas where sensibility is essential.     

End-to-side neurorrhaphy of sensory nerves

One century passed before end-to-side neurorrhaphy was rediscovered, and now it finds more frequent use in clinical practice. Experimental studies have improved our understanding of the underlying mechanism and its potential. However, still discussed is whether reinnervation by end-to-side neurorrhaphy works as well in sensory nerves as in motor nerves. The digital nerves are sensory nerves and therefore an ideal model to investigate this question. Two cases of successful sensory reinnervation by end-to-side nerve suture are reported. We began to use end-to-side nerve repair clinically in 1995 and have used it for motor or sensory reinnervation in a total of 13 cases. In two patients primary nerve repair using end-to-side neurorrhaphy was performed in digital avulsion injuries. In one patient the avulsed ulnar nerve of the thumb was sutured end-to-side to the median nerve; in the other the ulnar digital nerve of the ring finger had been destroyed over a distance of 20 mm, and the distal stump was joined end-to-side to the radial nerve of the same finger. Sensory recovery was obtained in both patients. The static two-point discrimination was 3.0 mm, and dynamic two-point discrimination was 2-3 mm for the reinnervated finger compared to 2 mm for static and dynamic two-point discrimination in the adjacent "donor" finger. The sensation of the finger supplied by the "donor nerve" was not altered in relation to the corresponding contralateral finger site. Excellent sensory reinnervation is possible through an end-to-side nerve suture. Proximal avulsion, missing proximal nerve stumps, partial recovery, and prevention of nerve grafts are good indications for resensitization using end-to-side neurorrhaphy. No harm to the donor nerve is expected. Preference should be given to donor nerves that supply skin areas near to the anesthetic area.     

The uroepithelial-associated sensory web

An important, but not well understood, function of epithelial cells is their ability to sense changes in their extracellular environment and then communicate these changes to the underlying nervous, connective, and muscular tissues. This communication is likely to be important for tube- and sac-shaped organs such as blood vessels, the lungs, the gut, and the bladder, whose normal function can be modulated by stimuli initiated within the epithelium. We propose that the uroepithelium, which lines the renal pelvis, ureters, and inner surface of the bladder, functions as an integral part of a 'sensory web.' Through uroepithelial-associated channels and receptors, the uroepithelium receives sensory 'inputs' such as changes in hydrostatic pressure and binding of mediators including adenosine triphosphate (ATP). These input signals stimulate membrane turnover in the outermost umbrella cell layer and release of sensory 'outputs' from the uroepithelium in the form of neurotransmitters and other mediators that communicate changes in the uroepithelial milieu to the underlying tissues, altering their function. The global consequence of this sensory web is the coordinated function of the bladder during the cycles of filling and voiding, and disruption of this web is likely to lead to bladder dysfunction.     

Bypassing primary sensory cortices--a direct thalamocortical pathway for transmitting salient sensory information

Detection and appropriate reaction to sudden and intense events happening in the sensory environment is crucial for survival. By combining Bayesian model selection with dynamic causal modeling of functional magnetic resonance imaging data, a novel analysis approach that allows inferring the causality between neural activities in different brain areas, we demonstrate that salient sensory information reaches the multimodal cortical areas responsible for its detection directly from the thalamus, without being first processed in primary and secondary sensory-specific areas. This direct thalamocortical transmission of multimodal salient information is parallel to the processing of finer stimulus attributes, which are transmitted in a modality-specific fashion from the thalamus to the relevant primary sensory areas. Such direct thalamocortical connections bypassing primary sensory cortices provide a fast and efficient way for transmitting information from subcortical structures to multimodal cortical areas, to allow the early detection of salient events and, thereby, trigger immediate and appropriate behavior.     

Motor and sensory mapping

Functional magnetic resonance imaging (fMRI) enhances the understanding of neuroanatomy and functions of the brain and is becoming an accepted brain-mapping tool for clinicians, researchers, and basic scientists alike. A noninvasive procedure with no known risks, fMRI has an ever-growing list of clinical applications, including presurgical mapping of motor, language, and memory functions. fMRI benefits patients and allows neurosurgeons to be aware of, and to navigate, the precise location of patient-specific eloquent cortices and structural anomalies from a tumor. Optimizing preoperative fMRI requires tailoring the fMRI paradigm to the patient's clinical situation and understanding the pitfalls of fMRI interpretation.     

Early compensatory sensory re-education

After a neurorrhaphy, there will be a distal disconnection between the cortex and skin receptors, along with interruption of sensibility information. This report demonstrates the efficacy of a new sensory re-education program for achieving optimal sensation in a relatively short time. Between 1999 and 2001, in the authors' Hand Rehabilitation Department, 11 patients with previous neurorrhaphy were subjected to a program of early "compensatory sensory re-education." Lesions were caused by clean cut. There were 13 primary digital nerve procedures, 12 at the distal palmar MP level, and one at the radial dorsal branch of the index (just after emerging from the common digital nerve). The technique of compensatory sensory re-education was based on a previous, but modified, sensory re-education method. In order to evaluate the results in the compensatory sensory re-education series described, additional tests for evaluation of achieved functional sensibility were used. The authors' best results were achieved in a maximum of 8 weeks (4-8 weeks), much less time than with the original method (1-2 years). Using the British classification, it was possible to compare the achieved levels of sensibility and the time required for optimal results. The different methods of sensibility re-education may be similar, but with the authors' compensatory sensory re-education method, substantial time is saved.     

Three-in-one blocks with ropivacaine: evaluation of sensory onset time and quality of sensory block

The purpose of this prospective, randomized, double-blinded study was to evaluate the sensory onset time and the quality of sensory block of ropivacaine, a new long-acting local anesthetic, compared with bupivacaine, for 3-in-1 blocks. Fifty ASA physical status I-III patients undergoing hip surgery after trauma were randomly assigned to two study groups of 25 patients each. The two study groups received a 3-in-1 block with either 20 mL of ropivacaine 0.5% or 20 mL of bupivacaine 0.5%. Blocks in both groups were performed using a nerve stimulator. The sensory onset time and the quality of sensory block was assessed by pinprick test in the central sensory region of each of the three nerves and compared with the same stimulation in the contralateral leg. We used a scale from 100% (normal sensation) to 0% (no sensory sensation). We did not find significant differences in sensory onset times between the ropivacaine group and the bupivacaine group (30+/-11 vs 32+/-10 min). The quality of sensory blocks was also comparable between the study groups (19%+/-20% vs 21%+/-15%). We conclude that the sensory onset time and quality of sensory block during 3-in-1 blocks performed with ropivacaine are comparable to those with bupivacaine. Ropivacaine is described as being less potent than bupivacaine, making this local anesthetic promising for 3-in-1 blocks because of its reportedly lower incidence of cardiovascular and central nervous system complications. IMPLICATIONS: Ropivacaine 0.5% has a sensory onset time and quality of sensory block during 3-in-1 blocks similar to that of bupivacaine 0.5%. Ropivacaine is described as being less potent than bupivacaine, making it a promising local anesthetic for 3-in-1 blocks because of its reportedly lower cardiovascular and central nervous system toxicity.     

Top-down modulation of early sensory cortex

Data from nine previous studies of human visual information processing using positron emission tomography were reanalyzed to contrast blood flow responses during passive viewing and active discriminations of the same stimulus array. The analysis examined whether active visual processing (i) increases blood flow in medial visual regions early in the visual hierarchy and (ii) decreases blood flow in auditory and somatosensory cortex. Significant modulation of medial visual regions was observed in six of nine studies, indicating that top-down processes can affect early visual cortex. Modulations showed several task dependencies, suggesting that in some cases the underlying mechanism was selective (e.g. analysis-or feature-specific) rather than non- selective. Replicable decreases at or near auditory Brodmann area (BA) left 41/42 were observed in two of five studies, but in different locations. Analyses that combined data across studies yielded modest but significant decreases. Replicable decreases were not found in primary somatosensory cortex but were observed in an insular region that may be a somatosensory association area. Decreases were also noted in the parietal operculum (perhaps SII) and BA 40. These results are inconsistent with a model in which the precortical input to task- irrelevant sensory cortical areas is broadly suppressed.      

Surgery modifies cardiac sensory transduction

OBJECTIVE: We sought to determine whether cardiac surgery, specifically the placement of an incision within a ventricular wall, affects the capacity of regional cardiac sensory nerve terminals (neurites) to transduce the local cardiac milieu. METHODS: The capacity of sensory neurites in the right ventricular outflow tract associated with afferent neurons in nodose ganglia to transduce their mechanical and chemical milieu was studied in 11 anesthetized pigs before and after performing a local ventriculotomy. RESULTS: Right ventricular outflow tract sensory neurites associated with 23 nodose ganglion afferent neurons were identified that transduced local mechanical deformation along with substance P. The capacity of these sensory neurites to transduce these stimuli was almost totally obtunded after local ventriculotomy. CONCLUSIONS: The capacity of afferent neurons to transduce the cardiac milieu can be modified by cardiac surgical interventions. This may have negative implications with respect to how the entire cardiac neuronal hierarchy transduces alterations in the cardiac milieu postsurgery. This fact should be taken into account when contemplating the placement of cardiac incisions during surgery.     

Resurfacing and sensory recovery of the sole

(1) There is very little quantitative objective information on sensory recovery after resurfacing of the sole. However, based on results obtained by quantitative rather than qualitative methods to measure sensibility, there is little reason to expect a high level of sensory recovery, at least in free flaps. There is no evidence to prove or refute that by using neurosensory flaps or other forms of neurotization, a higher level of sensibility can be achieved, and therefore no reason why such a flap should be specifically selected when reconstructing the sole. Also, the sensibility of the flap has not been shown to be related to the soft-tissue stability after resurfacing of traumatic defects. (2) There are no firm guidelines to flap selection. If possible, a local flap should be selected. If a free-tissue transfer is necessary, a safe choice is for the surgeon to select a familiar flap with a long pedicle of sufficient caliber. The flap should be well tailored into the defect, and excessively thick flaps should be avoided. If in doubt, the donor area can be measured with ultrasonography and compared with the depth of the defect. Muscle flaps should be used to cover deep, irregular, or infected defects, whereas skin flaps are suitable for resurfacing superficial degloving tissue loss. (3) The most important reason for recurrent breakdowns after reconstruction may be abnormally high pressure points in the sole. Bony deformities should be identified preoperatively and removed during the operation. Patient education in meticulous foot care and custom-made insoles or footwear should be provided to prevent reulcerations. (4) The ideal method of resurfacing of the sole would also provide normal sensibility to the skin. With free-flap transfer this cannot be achieved with current techniques. Before new methods of neural reconstruction can be recommended for general use, their efficacy in improving sensibility should be documented by prospective studies using quantitative methods of measurement. If a reduction of breakdowns is claimed, biomechanical studies should be employed to exclude this being merely due to elimination of abnormal pressure points in the sole.     

Both stump area and volume of distal sensory nerve segments influence the regeneration of sensory axons in rats.

We examined the influence of both stump area and volume of a distal sensory nerve segment on neurotropic induction of regenerating sensory axons in a rat saphenous nerve model. In group 1 (n = 10) the proximal stump of the severed saphenous nerve was inserted into the proximal channel, and a 2 cm free nerve segment and a double-barrelled 1 cm free nerve segment were inserted into the distal two channels of a silicone Y-chamber. In group 2 (n = 10), 2 cm and 1 cm free nerve segments were inserted into the distal two channels of a Y-chamber. The gap between the stumps was set at 4 mm. After six weeks, we counted and compared the number of regenerated myelinated sensory axons in the distal two channels. Significantly more axons regenerated in the wider stump area channel of group 1 and in the larger volume channel of group 2 than in the opposite channel in either group (p < 0.05 in each case).