Repetitive peripheral magnetic stimulation for the assessment of wrist spasticity: reliability, validation and correlation with clinical measures.

PURPOSE: To determine feasibility and reliability of using repetitive peripheral magnetic stimulation (rPMS) to induce wrist extension movement for the assessment of spasticity in wrist flexors, instead of the passive stretch used in the modified Tardieu scale. METHODS: Spasticity was assessed with the index of movement restriction (iMR), calculated as the difference between the range of maximum wrist passive movement and the rPMS-induced movement, in 12 healthy subjects (HS), 12 acute stroke patients without spasticity (AS) and 12 chronic stroke patients with spasticity (CS). Test-retest reliability and clinical correlation were assessed in CS patients before Botulinum neurotoxin type A (BoNT-A) treatment. RESULTS: In comparison to HS and AS patients, CS patients showed statistically significant reduction of rPMS-induced movement amplitude, velocity, and acceleration. The mean iMR was 2.8 (SD = 2.6) in HS, 13.0 (SD = 11.2) in AS and 59.2 (SD = 23.4) in CS. This score significantly reduced to 41.1 (SD = 19.7) in CS after BoNT-A (p < 0.01). Test-retest reliability was very good, with an intraclass correlation coefficient ranging between 0.85 and 0.99 for the variables analysed. CONCLUSIONS: We have shown good reliability and feasibility of a new method providing quantifiable data for the assessment of spasticity and its response to BoNT-A treatment.IMPLICATIONS FOR REHABILITATIONThe muscle contraction induced by repetitive peripheral magnetic stimulation (rPMS) in paretic muscles of post-stroke patients was used to assess spasticity.The index of movement restriction (iMR), calculated as the difference between the maximum passive range of movement and the rPMS induced movement, improved after botulinum toxin treatment.Measuring spastic reactions to rPMS provides quantifiable and reliable data for follow-up and assessment of therapeutic benefits.

Sensory processing in Huntington's disease.

OBJECTIVE: An intriguing electrophysiological feature of patients with Huntington's disease (HD) is the delayed latency and decreased amplitude of somatosensory long-latency evoked potentials (LLeps). We investigated whether such dysfunction was associated with delayed conscious perception of the sensory stimulus. METHODS: Sixteen HD patients and 16 control subjects faced a computer screen showing the Libet's clock (Libet et al., 1983). In Rest trials, subjects had to memorize the position of the clock handle at perception of either electrical or thermal stimuli (AW). In React, additionally, they were asked to make a fist with their right hand, in a simple reaction time task (SRT). LLseps were recorded from Cz in both conditions. RESULTS: LLeps negative peak latency (N2) and SRT were abnormally delayed in patients in all conditions. AW was only abnormally prolonged in the React condition but the time difference between AW and the negative peak of the LLeps was not different in the two groups. There was a significant negative correlation between SRT and AW or LLeps amplitude in patients but not in healthy subjects. CONCLUSION: Our HD patients did not show abnormalities in conscious perception of sensory stimuli but their LLeps abnormalities were more marked when they had to react. This is compatible with failure to detect stimulus salience rather than with a cognitive defect. SIGNIFICANCE: HD patients at early stages of the disease have preserved subjective perception of sensation but faulty sensorimotor integration.

Transcranial Direct Current Stimulation (tDCS) Enhances the Excitability of Trigemino-Facial Reflex Circuits.

BACKGROUND: Transcranial direct current stimulation (tDCS) causes a tiny burning sensation through activation of local cutaneous trigeminal afferents. HYPOTHESIS: Trigeminal sensory inputs from tDCS may generate excitability changes in the trigemino-facial reflex circuits. OBJECTIVES AND METHODS: Sixteen healthy volunteers were submitted to 20 minutes tDCS sessions with two types of electrode-montage conditions: 1. Real vs Sham 'bi-hemispheric' tDCS (cathode/anode: C4/C3), for blinded assessment of effects, and 2. 'uni-hemispheric' tDCS (cathode/anode: Fp3/C3), for assessment of laterality of the effects. Supraorbital nerve stimuli were used to obtain blink reflexes before, during (10 minutes from onset) and after (30 minutes from onset) the tDCS session. Outcome measures were R2 habituation (R2H) to repeated stimuli, the blink reflex excitability recovery (BRER) to paired stimuli and the blink reflex inhibition by a prepulse (BRIP). RESULTS: Real but not sham bi-hemispheric tDCS caused a significant decrease of R2H and leftward shift of BRER curve (p < 0.05 for all measures). The effects of uni-hemispheric tDCS on BRER and BRIP were larger on ipsilateral than on contralateral blink reflexes (p < 0.05). Excitability changes were still present 10 minutes after the end of stimulation in a lesser extent. CONCLUSIONS: This study shows that 20 minute tDCS enhances the excitability of trigemino-facial reflex circuits. The finding of larger ipsilateral than contralateral effects suggests that sensitization through cutaneous trigeminal afferents adds on other possible mechanisms such as activation of cortico-nuclear or cortico-reticular connections.

Cutaneous autonomic denervation in Parkinson's disease.

Numerous studies have detailed involvement of the peripheral autonomic nervous system (PANS) in Parkinson's disease (PD). We assessed autonomic innervation of dermal annexes through quantitative fluorescence measurement from skin obtained via punch biopsies at distal leg region in PD and control subjects. We defined a ratio between the area corresponding to protein gen product (PGP) immunoreactivity and the area corresponding to blood vessel or sweat gland as a quantitative measure of autonomic innervation. Presence of alpha-synuclein (AS) deposits in dermis and hypodermis was also assessed by immunohistochemistry. Skin biopsies form six PD patients and six healthy controls were studied. Autonomic innervation scores were lower in PD than in controls in both blood vessels and sweat glands. No AS or phosphorylated AS (pAS) immunoreactivity was detected in dermis or hypodermis in any of the studied subjects. The results of this investigation suggest that autonomic innervation of dermal annexes in living patients with PD is reduced compared to controls. AS or pAS deposits were not found in dermis or hypodermis suggesting that distal leg skin study is not useful for in vivo detection of AS in PD.

The effects of transcranial direct current stimulation on conscious perception of sensory inputs from hand palm and dorsum.

Conscious perception of sensory signals depends in part on stimulus salience, relevance and topography. Letting aside differences at skin receptor level and afferent fibres, it is the CNS that makes a contextual selection of relevant sensory inputs. We hypothesized that subjective awareness (AW) of the time at which a sensory stimulus is perceived, a cortical function, may be differently modified by cortical stimulation, according to site and type of the stimulus. In 24 healthy volunteers, we examined the effects of transcranial direct current stimulation (tDCS) on the assessment of AW to heat pain or weak electrical stimuli applied to either the hand palm or dorsum. We also recorded the vertex-evoked potentials to the same stimuli. The assessment was done before, during and after cathodal or anodal tDCS over the parietal cortex contralateral to the hand receiving the stimuli. At baseline, AW to thermal stimuli was significantly longer for palm than for dorsum (P < 0.01), while no differences between stimulation sites were observed for the electrical stimuli. Both cathodal and anodal tDCS caused a significant shortening of AW to thermal stimuli in the palm but not in the dorsum, and no effects on AW to electrical stimuli. Longer AW in the palm than in the dorsum may be attributable to differences in skin thickness. However, the selectivity of the effects of tDCS on AW to thermal stimulation of the glabrous skin reflects the specificity of CNS processing for site and type of sensory inputs.

Disturbed sensory perception of changes in thermoalgesic stimuli in patients with small fiber neuropathies.

The assessment of functional deficits in small fibre neuropathies (SFN) requires using ancillary tests other than conventional neurophysiological techniques. One of the tests with most widespread use is thermal threshold determination, as part of quantitative sensory testing. Thermal thresholds typically reflect one point in the whole subjective experience elicited by a thermal stimulus. We reasoned that more information could be obtained by analyzing the subjective description of the ongoing sensation elicited by slow temperature changes (dynamic thermal testing, DTT). Twenty SFN patients and 20 healthy subjects were requested to describe, by using an electronic visual analog scale system, the sensation perceived when the temperature of a thermode was made to slowly change according to a predetermined pattern. The thermode was attached to the left ventral forearm or the distal third of the left leg and the stimulus was either a monophasic heat or cold stimuli that reached 120% of pain threshold and reversed to get back to baseline at a rate of 0.5 °C/s. Abnormalities seen in patients in comparison to healthy subjects were: (1) delayed perception of temperature changes, both at onset and at reversal, (2) longer duration of pain perception at peak temperature, and (3) absence of an overshoot sensation after reversal, ie, a transient perception of the opposite sensation before the temperature reached again baseline. The use of DTT increases the yield of thermal testing for clinical and physiological studies. It adds information that can be discriminant between healthy subjects and SFN patients and shows physiological details about the process of activation and inactivation of temperature receptors that may be abnormal in SFN.

Mitochondrial loss indicates early axonal damage in small fiber neuropathies.

Evaluation of nerve fibers in the skin provides a useful tool for the diagnosis of small fiber neuropathies (SFNs). Our aim was to determine whether mitochondria are involved in SFN, indicating early axonal damage. We quantified mitochondrial respiratory chain complex IV (OXPHOS) and axonal (PGP 9.5) fluorescence on skin sections from 32 SFN patients and 14 healthy controls. Also, a group of six patients were recruited before and after 30-day treatment with the mitotoxic antibiotic linezolid. We measured the co-localization of OXPHOS within the intraepidermal and subpapillary dermal axons (PGP-immunoreactive [PGP-ir]). SFN patients with relatively preserved intraepidermal nerve fibers (SFN borderline) showed statistically significant reduction of OXPHOS (50.5 ± 33.9 µm(2) vs. 107.6 ± 81 µm(2) in controls, p < 0.02). A positive correlation was found between both PGP-ir and OXPHOS in controls (Pearson's coefficient r = 0.59, p < 0.001), whereas such correlation was absent in SFN. With respect to baseline measurements, linezolid therapy increased both PGP-ir and OXPHOS, which could be considered an initial compensatory toxic-induced response. This study set out to identify a possible marker of axonal pre-degenerative state in SFN borderline patients.

Epidermal Langerhans cells in small fiber neuropathies.

We quantified the immune histiocytic Langerhans cells (LCs) in skin biopsy samples of patients with distal small fiber neuropathy (SFN). Patients were divided according to the presence or absence of neuropathic pain (burning pain) assessed by a visual analogue scale (VAS). We studied 13 diabetic patients (pain-DSFN), 7 nondiabetic patients (pain-SFN) who reported relevant neuropathic pain (VAS ≥ 3), and 6 nondiabetic patients without neuropathic pain (no-pain-SFN). Using double immunofluorohistochemistry with the PGP 9.5 and the langerin/CD207, we quantified the intraepidermal nerve fibers density (IENFD) and LCs per square millimeter in the epidermis. A group of 10 skin samples from healthy subjects served as controls. Confocal analysis was performed to evaluate LC PGP 9.5-immunoreactivity. We found a mean value of 334.3LC/mm(2) in controls, 310.2LC/mm(2) in no-pain-SFN, 329.6LC/mm(2) in pain-SFN and 484.3LC/mm(2) in pain-DSFN (analysis of variance; P=.01). In patients, analysis of covariance adjusted by different covariables showed that the presence of diabetes (F=5.2, P=.03) was associated with an increased number of LC/mm(2). There was a negative correlation between the IENFD and the number of LCs (r(2)=-0.13, P=.03). No statistically significant differences were found among groups of subjects either for the co-localization or for the number of LCs that were PGP 9.5-immunoreactive (analysis of variance; P>.05). These results indicate that patients with neuropathic pain in the context of SFN, specially those who had diabetes (DSFN), had an increased number of LCs in the epidermis that may play a role in the generation or maintenance of neuropathic pain.

Axonal fluorescence quantitation provides a new approach to assess cutaneous innervation.

We present a novel approach to quantify skin innervation by measuring the PGP 9.5 immunoreactive (PGP-ir) fluorescence corresponding to axons within the epidermis and dermis. The skin biopsies from 35 controls and 45 small fiber neuropathy (SFN) patients were included. In 50-µm free-floating sections, we determined the intraepidermal nerve fiber density (IENFD) by direct fluorescence visualization and captured 2-µm thick individual optical sections using the same confocal microscope and magnification. We measured the fluorescence of the PGP-ir axons in both, epidermal and dermal area by using the ImageJ software. There was good interobserver and intraobserver reliability of PGP-ir measures, similar than for IENFD. The PGP-ir axons were found decreased in patients with SFN (1.1‰ and 9.0‰ respectively for epidermal and dermal area in contrast to 2.2‰ and 16.0‰, respectively to controls). The area under the ROC curve was 0.90 for the IENFD, 0.84 for epidermal PGP-ir axons and 0.70 for dermal PGP-ir axons. There was a positive correlation between the IENFD and the PGP-ir axons at epidermis (Spearman Rho=0.66, p<0.001) as well as for the dermal nerve length and the PGP-ir axons at dermis (Spearman Rho=0.45, p<0.05). This method is also particularly adequate for the quantitation of dermal nerve fibers. We conclude that quantifying the fluorescent PGP-ir axons could help to assess skin innervation (dermal and epidermal nerve fibers) in patients with SFN.

On the relationship between nociceptive evoked potentials and intraepidermal nerve fiber density in painful sensory polyneuropathies.

This study analyzed the relationship between the density of intraepidermal nerve fibers (IENF) and the characteristics of either nociceptive laser-evoked potentials (LEPs) or contact heat-evoked potentials (CHEPs) in patients with painful sensory polyneuropathy with the aim to determine which parameters of LEPs and CHEPs more reliably reflect IENF loss. A total of 96 patients and 35 healthy volunteers took part in the study. Based on clinical examination, nerve conduction tests, and quantitative sensory testing, we identified 52 patients with small-fiber neuropathy (SFN), 40 with mixed (small-fiber and large-fiber) neuropathy (MFN), and 4 who were excluded from the analysis because of no evidence of involvement of small fibers. The latency of the N2 was delayed for both LEPs and CHEPs in patients with MFN and for CHEPs only in patients with SFN. The amplitude of the vertex N2/P2 potential was similarly reduced in both types of neuropathy, but LEPs were more frequently absent than CHEPs in MFN patients (68% vs 40%). In general, latency and amplitude of LEPs and CHEPs were well correlated with IENF density. SFN patients were characterized by abnormal EPs and slightly decreased but morphologically abnormal IENF. MFN patients were characterized by frequently absent LEPs and CHEPs and a rather severe IENF loss. The correlation between nociceptive evoked potentials (laser-evoked potentials and contact heat-evoked potentials) and skin biopsy aids in the diagnosis of painful neuropathies.