Pain thresholds as a putative functional test for cerebral laterality in major depressive disorder and panic disorder

Multi-Region Microdialysis Imaging Platform Revealed Dorsal Raphe Nucleus Calcium Signaling and Serotonin Dynamics during Nociceptive Pain

In this research, we combined our ultralight micro-imaging device for calcium imaging with microdialysis to simultaneously visualize neural activity in the dorsal raphe nucleus (DRN) and measure serotonin release in the central nucleus of the amygdala (CeA) and the anterior cingulate cortex (ACC). Using this platform, we observed brain activity following nociception induced by formalin injection in the mouse’s hind paw. Our device showed that DRN fluorescence intensity increased after formalin injection, and the increase was highly correlated with the elevation in serotonin release in both the CeA and ACC. The increase in calcium fluorescence intensity occurred during the acute and inflammatory phases, which suggests the biphasic response of nociceptive pain. Furthermore, we found that the increase in fluorescence intensity was positively correlated with mouse licking behavior. Lastly, we compared the laterality of pain stimulation and found that DRN fluorescence activity was higher for contralateral stimulation. Microdialysis showed that CeA serotonin concentration increased only after contralateral stimulation, while ACC serotonin release responded bilaterally. In conclusion, our study not only revealed the inter-regional serotonergic connection among the DRN, the CeA, and the ACC, but also demonstrated that our device is feasible for multi-site implantation in conjunction with a microdialysis system, allowing the simultaneous multi-modal observation of different regions in the brain.

A Systematic Review of Thermosensation and Thermoregulation in Anxiety Disorders

Objectives: Sweating, hot flushes, and blushing are symptoms frequently reported by individuals with anxiety disorders. They represent important reinforcers of anxiogenic cognitions and behaviours. One system that may be involved in the manifestation of these symptoms is the thermosensory/thermoregulatory system. The aim of the present study was to investigate to what extent individuals with anxiety disorders are characterised by alterations in this system.

Methods: PubMed and PsycINFO were systematically searched. Studies were eligible if they (i) assessed individuals with anxiety disorders, (ii) thermosensation or thermoregulatory effectors/outcomes, and (iii) used a case-control design.

Results:N = 86 studies were identified. There was no evidence of altered thermosensation in individuals with anxiety disorders. Regarding thermoregulatory effectors, individuals with social anxiety disorder exhibited altered cutaneous vasodilation upon pharmacological challenge; individuals with specific phobia showed increased sweating upon confrontation with phobic stimuli; individuals with panic disorder showed increased daily sweating as well as increased sweating in response to non-phobic and phobic stimuli. Regarding thermoregulatory outcomes, there was evidence for altered skin temperature in all subtypes of anxiety.

Conclusion: Whereas there was no evidence of altered thermoregulation in specific phobia, a subgroup of individuals with social anxiety and panic disorder appears to exhibit altered vasodilation and sweating, respectively. Longitudinal research is warranted to investigate whether this represents a vulnerability to anxiety/panic.

Altered physical pain processing in different psychiatric conditions

Several reports indicate either increased or decreased pain sensitivity associated with psychiatric disorders. Chronic pain is highly prevalent in many of these conditions. We reviewed the literature regarding experimental pain sensitivity in patients with major depression, bipolar disorder, posttraumatic stress disorder (PTSD), generalized anxiety disorder, panic disorder, obsessive-compulsive disorder and schizophrenia. Electronic searches were performed to identify studies comparing experimental pain in patients with these conditions and controls. Across 31 depression studies, reduced pain threshold was noted except for ischemic stimuli, where increased pain tolerance and elevated sensitivity to ischemic pain was observed. A more pervasive pattern of low pain sensitivity was found across 20 schizophrenia studies. The majority of PTSD studies (n = 20) showed no significant differences compared with controls. The limited number of bipolar disorder (n = 4) and anxiety (n = 9) studies precluded identification of clear trends. Wide data variability was observed. Awareness of psychiatric patients' pain perception abnormalities is needed for active screening and addressing physical comorbidities, in order to enhance quality of life, life expectancy and mental health.

Brain Asymmetry: Towards an Asymmetrical Neurovisceral Integration

Despite the ancestral evidence of an asymmetry in motor predominance, going through the inspiring discoveries of Broca and Wernicke on the localization of language processing, continuing with the subsequent noise coinciding with the study of brain function in commissurotomized patients—and the subsequent avalanche of data on the asymmetric distribution of multiple types of neurotransmitters in physiological and pathological conditions—even today, the functional significance of brain asymmetry is still unknown. Currently, multiple evidence suggests that functional asymmetries must have a neurochemical substrate and that brain asymmetry is not a static concept but rather a dynamic one, with intra- and inter-hemispheric interactions between its various processes, and that it is modifiable depending on changing endogenous and environmental conditions. Furthermore, based on the concept of neurovisceral integration in the overall functioning of an organism, some evidence has emerged suggesting that this integration could be organized asymmetrically, using the autonomic nervous system as a bidirectional communication pathway, whose performance would also be asymmetric. However, the functional significance of this distribution, as well as the evolutionary advantage of an asymmetric nervous organization, is still unknown.

Spinal and Cerebral Integration of Noxious Inputs in Left-handed Individuals

Some pain-related information is processed preferentially in the right cerebral hemisphere. Considering that functional lateralization can be affected by handedness, spinal and cerebral pain-related responses may be different between right- and left-handed individuals. Therefore, this study aimed to investigate the cortical and spinal mechanisms of nociceptive integration when nociceptive stimuli are applied to right -handed vs. left -handed individuals. The NFR, evoked potentials (ERP: P45, N100, P260), and event-related spectral perturbations (ERSP: theta, alpha, beta and gamma band oscillations) were compared between ten right-handed and ten left-handed participants. Pain was induced by transcutaneous electrical stimulation of the lower limbs and left upper limb. Stimulation intensity was adjusted individually in five counterbalanced conditions of 21 stimuli each: three unilateral (right lower limb, left lower limb, and left upper limb stimulation) and two bilateral conditions (right and left lower limbs, and the right lower limb and left upper limb stimulation). The amplitude of the NFR, ERP, ERSP, and pain ratings were compared between groups and conditions using a mixed ANOVA. A significant increase of responses was observed in bilateral compared with unilateral conditions for pain intensity, NFR amplitude, N100, theta oscillations, and gamma oscillations. However, these effects were not significantly different between right- and left-handed individuals. These results suggest that spinal and cerebral integration of bilateral nociceptive inputs is similar between right- and left-handed individuals. They also imply that pain-related responses measured in this study may be examined independently of handedness.

Migraine Pain Location and Measures of Healthcare Use and Distress: An Observational Study

Introduction

Lateralized pain is a core diagnostic feature of migraine. In previous research, left-sided spinal pain was more frequent and associated with greater emotional distress and healthcare use than right-sided pain. We hypothesized therefore that patients with left-sided head pain might experience higher levels of distress or healthcare use than those with right-sided or bilateral pain.

Methods

Medical record information was extracted for 477 randomly selected patients with migraine seen in 2011 in a tertiary headache clinic. This included demographic data, pain location, handedness, comorbid psychiatric diagnoses, medical and emergency department visits, and use of selected headache medications.

Results and Discussion

Two hundred twenty-eight of four hundred seventy-seven (47.8%) patients reported lateralized pain, of which 107 (47.9%) patients were right sided compared with 65 (28.5%) left-sided patients (p=0.001), while 56 (24.5%) reported unilateral pain with no side predominance. Contrary to expectations, with the exception of self-reported posttraumatic stress disorder, there were no statistically significant differences between left and right in measures of psychiatric distress, emergency department visits, or healthcare use.

Conclusion

Although unilateral pain location can be helpful in making a migraine diagnosis, it does not appear to have additional clinical implications. Additionally, its absence does not rule out a diagnosis of migraine since more than half of migraineurs have bilateral head pain.

Left/Right Pain Asymmetry With Injectable Cosmetic Treatments for the Face

BACKGROUND

Pain is processed and experienced differently on the left (L) and right (R) sides of the body; however, L/R pain asymmetry with cosmetic treatments of the face has not been evaluated.

OBJECTIVES

The authors compared patient ratings of L/R facial pain during and immediately after injectable cosmetic treatments.

METHODS

In this cross-sectional multicenter pragmatic study, pain levels were evaluated for 302 patients who underwent facial treatments with botulinum toxin (BTX) and/or impermanent soft-tissue filler (STF). Patients indicated pain intensity on each side of the face with a visual analogue scale (VAS; 0, no pain; 10, worst pain).

RESULTS

Combined mean VAS scores for BTX and STF treatments (L, 3.79 vs R, 3.42), and individual scores for BTX (L, 3.60 vs R, 3.30) or STF (L, 4.22 vs R, 3.69) treatments were significantly different, with pain rated as worse on the L side of the face (all P < 0.01). When treatments were performed first on the L side, patients rated the overall experience as significantly less painful than when treatments were begun on the R side. BTX treatments with a 29-gauge (G) needle were significantly more painful than with a 33-G needle.

CONCLUSIONS

To lessen pain with injectable facial treatments, the authors recommend placing the first injection on the L side of the face and, when possible, employing a high-G needle.

LEVEL OF EVIDENCE 2

Is Pain Perception Altered in People With Depression? A Systematic Review and Meta-Analysis of Experimental Pain Research

Although clinical studies suggest depressed patients may be more vulnerable to pain, experimental research is equivocal. This meta-analysis aimed to clarify whether depression is associated with altered pain perception in response to noxious stimulation and to identify factors that might influence this association. A search of major electronic databases was conducted to identify experimental studies investigating pain response in depressed participants versus healthy control participants using established pain outcome measures. Random effects meta-analysis of standardized mean differences was conducted on data from 32 studies (N = 1,317). For high-intensity noxious stimulation, overall pain tolerance was similar across depressed and control groups (Hedges g = .09, P = .71, studies = 10). For low-intensity stimulation, a small, but statistically significant higher mean sensory threshold (g = .35, P = .01, studies = 9) and pain threshold (g = .32, P = .02, studies = 25) was observed in depressed participants, suggesting diminished pain. However, considerable heterogeneity in the direction and magnitude of effects was observed, indicating a likely condition-specific effect of depression on pain. Subgroup analysis found that pain threshold/tolerance was increased in depression for exteroceptive (cutaneous) stimulation but decreased for interoceptive (ischemic) stimulation, but that substantial heterogeneity remained. Overall, results provide some support for altered pain processing in depression, but suggest this link is dependent upon modality and additional, unidentified factors.

PERSPECTIVE

This meta-analysis of experimental studies suggests potential effects of depression on pain perception are variable and likely to depend upon multiple factors. The contrasting pattern for ischemic versus other noxious stimuli suggests that stimulus modality is a key factor, which could help explain discrepancies across clinical and experimental findings.

Experimental pain sensitivity in subjects with major depression: Many pain complaints without hypersensitivity

OBJECTIVE

Patients with major depression frequently complain of pain, but conflicting data exist concerning their changes in pain sensitivity. This study aimed at comparing the sensitivity to moderate controlled pain between subjects presenting a major depressive episode (isolated and recurrent depressive episodes or a bipolar disorder), controls, and subjects with schizophrenia from a previous study.

METHOD

Pain sensitivity was assessed obtaining the visual analog scale (VAS) rating for the application of a 160 kPa pre-fixed pressure (fpVAS), the pressure corresponding to a VAS score of 3, and the time required to achieve a VAS score of 3 during ischemia induction. The effects of depression intensity, alexithymia, current and past general pain, and of six weeks of antidepressant treatment on fpVAS were investigated.

RESULTS

The results did not differ significantly between the depressed groups and the controls, without any effect of depression intensity. Presence of long-lasting pain and current pain felt on the day of testing correlated with fpVAS. The subjects of the depressed group were less sensitive than subjects with schizophrenia. FpVAS was significantly lower before and after antidepressant treatment in the subjects presenting clinical improvement.

CONCLUSIONS

No difference in experimental pain sensitivity and expression between major depressive episode subjects and controls, in opposite to pain complaints, is to be detected. The changes in the sensation of pain routinely attributed to subjects presenting depression may result from changes in a differential processing of pain signals, not in relation with the depression intensity, or the kind of depressive disorder.

Measuring mechanical pain: the refinement and standardization of pressure pain threshold measurements

Pain thresholds are widely used in behavioral research, but unlike other pain modalities, a standardized assessment of pressure pain remains a challenge. In this research, we describe the application of an automatic pressure algometer with a linear increase in force. Ergonomically designed fixation devices were developed to increase the accuracy and to shorten the time of each measurement. Ten healthy volunteers were included in a pilot study to test the algometry method. Pressure pain thresholds (PPTs) were investigated over 2 experimental days in three nonconsecutive runs at 29 measurement sites. During the experiment, subjects reported their subjective sleepiness, level of state-anxiety, psychological status and the perceived pain intensity of each measurement. Pain intensity ratings indicate that instructions were followed. State-anxiety and subjective sleepiness levels were low throughout the experiment. The method has proven to be suitable for standardized PPT measurements across the body in an ergonomic, safe, and user-friendly fashion.

Neuropsychological impairments in panic disorder: a systematic review

BACKGROUND

There is a growing body of literature investigating the neuropsychological profile of panic disorder (PD), some of which suggests potential cognitive dysfunction. This paper systematically reviews the existing literature on neuropsychological performance in PD.

METHOD

PsycINFO, EMBASE, MEDLINE and PsycARTICLES databases were searched to identify articles reporting on neuropsychological function in PD published in English during the time period 1980 to March 2012. 14 studies were identified.

RESULTS

There was limited support for impairment in short term memory among individuals with PD, although this was not found across all studies. Overall, the reviewed studies did not support the presence of impairment in other areas of cognitive functioning, including executive function, long term memory, visuospatial or perceptual abilities and working memory.

LIMITATIONS

Studies with samples of fewer than 15 participants per group were excluded from this review. A limited amount of research has been published on this topic and small sample sizes (under 25 per group) have been used by many studies. Therefore, the current review is based on a small number of studies with limited power.

CONCLUSIONS

There is limited evidence of specific neuropsychological impairments in participants with PD. Impairments in short term memory warrant further investigation to establish their relevance to clinical practice. Larger sample sizes and appropriate statistical adjustment for multiple comparisons in future studies is highly recommended.

Cerebral serotonin transporter asymmetry in females, males and male-to-female transsexuals measured by PET in vivo

The serotonergic system modulates brain functions that are considered to underlie affective states, emotion and cognition. Several lines of evidence point towards a strong lateralization of these mental processes, which indicates similar asymmetries in associated neurotransmitter systems. Here, our aim was to investigate a potential asymmetry of the serotonin transporter distribution using positron emission tomography and the radioligand [(11)C]DASB in vivo. As brain asymmetries may differ between sexes, we further aimed to compare serotonin transporter asymmetry between females, males and male-to-female (MtF) transsexuals whose brains are considered to be partly feminized. Voxel-wise analysis of serotonin transporter binding in all groups showed both strong left and rightward asymmetries in several cortical and subcortical structures including temporal and frontal cortices, anterior cingulate, hippocampus, caudate and thalamus. Further, male controls showed a rightward asymmetry in the midcingulate cortex, which was absent in females and MtF transsexuals. The present data support the notion of a lateralized serotonergic system, which is in line with previous findings of asymmetric serotonin-1A receptor distributions, extracellular serotonin concentrations, serotonin turnover and uptake. The absence of serotonin transporter asymmetry in the midcingulate in MtF transsexuals may be attributed to an absence of brain masculinization in this region.

Impact of visual learning on facial expressions of physical distress: a study on voluntary and evoked expressions of pain in congenitally blind and sighted individuals

The ability to facially communicate physical distress (e.g. pain) can be essential to ensure help, support and clinical treatment for the individual experiencing physical distress. So far, it is not known to which degree this ability represents innate and biologically prepared programs or whether it requires visual learning. Here, we address this question by studying evoked and voluntary facial expressions of pain in congenitally blind (N=21) and sighted (N=42) individuals. The repertoire of evoked facial expressions was comparable in congenitally blind and sighted individuals; however, blind individuals were less capable of facially encoding different intensities of experimental pain. Moreover, blind individuals were less capable of voluntarily modulating their pain expression. We conclude that the repertoire of facial muscles being activated during pain is biologically prepared. However, visual learning is a prerequisite in order to encode different intensities of physical distress as well as for up- and down-regulation of one's facial expression.

Depression and the hyperactive right-hemisphere

Depression is associated with an inter-hemispheric imbalance; a hyperactive right-hemisphere (RH) and a relatively hypoactive left-hemisphere (LH). Nevertheless, the underlying mechanisms which can explain why depression is associated with a RH dominance remain elusive. This article points out the potential links between functional cerebral asymmetries and specific symptoms and features of depression. There is evidence that the RH is selectively involved in processing negative emotions, pessimistic thoughts and unconstructive thinking styles--all which comprise the cognitive phenomenology of depression and in turn contribute to the elevated anxiety, stress and pain associated with the illness. Additionally, the RH mediates vigilance and arousal which may explain the sleep disturbances often reported in depression. The RH had also been linked with self-reflection, accounting for the tendency of depressed individuals to withdraw from their external environments and focus attention inward. Physiologically, RH activation is associated with hyprecortisolemia, which contributes to the deterioration of the immune system functioning and puts depressed patients at a greater risk of developing other illnesses, accounting for depression's high comorbidity with other diseases. Conversely, the LH is specifically involved in processing pleasurable experiences, and its relative attenuation is in line with the symptoms of anhedonia that characterize depression. The LH is also relatively more involved in decision-making processes, accounting for the indecisiveness that is often accompanied with depression.

Increased cold-pain thresholds in major depression

Most previous studies indicated that patients suffering from major depressive disorder (MDD) showed a decreased sensitivity for external or skin surface pain, eg, for heat or electrical stimuli, as compared to healthy controls. Here, we investigated cold-pain thresholds in 20 unmedicated patients suffering from MDD and 20 matched controls. We applied the ascending method of limits which has previously been used for heat-pain assessment in patients with depression. Similar to previous results for heat-pain thresholds we found a decreased sensitivity for cold pain in patients with MDD as indicated by increased cold-pain thresholds. This difference was significant on the right arm, whereas only a trend was obtained on the left arm, thus suggesting a certain degree of lateralization, similar to that seen in heat-pain perception in patients suffering from MDD or adjustment disorder. The study confirms our previous results of a lower sensitivity for externally induced pain in patients with MDD. Moreover, it adds weight to the assumption of a lateralized perception of thermal pain in depression.

PERSPECTIVE

This investigation provides further evidence for reduced pain perception of externally applied stimuli in major depression. Thus, central-nervous correlates for this altered pain perception in major depression are worth examining in future studies in order to gain more insight into mechanisms of pain perception on the one hand, and pathology of depression on the other.

Depression and changed pain perception: hints for a central disinhibition mechanism

Although patients with a depressive disorder report often of pain, their sensitivity to experimental pain is controversial, probably due to differences in sensory testing methods and to the lack of normal values. Therefore, we used a standardized and validated comprehensive sensory testing paradigm to assess the peripheral and central nervous system performance in depressive patients compared to healthy controls and chronic pain patients with fibromyalgia syndrome (FMS), in which depression is a common comorbidity. Twenty-five depressive psychiatric inpatients (pain-free: n=20), 35 FMS outpatients and 25 healthy controls underwent quantitative sensory testing (QST), including thermal and mechanical detection and pain thresholds, pain sensitivity and responsiveness to repetitive noxious mechanical stimuli (wind-up). In depressive disorder (to a lesser extent also in FMS), significantly decreased cold pain thresholds and an increased wind-up were found, although the mechanical pain thresholds and pain sensitivity were comparable to those of the healthy controls. All the detection thresholds were within the normal range in all the groups. In depressive disorder, there were no significant side differences in the detection and pain thresholds. The results contradict the former assumption of a general insensitivity to experimental pain in depressive disorder. In the mostly pain-free patients signs of an enhanced central hyperexcitability are even more pronounced than usually found in chronic pain patients (e.g. FMS), indicating common mechanisms in depressive disorder and chronic pain in accordance with the assumption of non-pain associated mechanisms in depressive disorder for central hyperexcitability, e.g. by inhibited serotonergic function. Furthermore, this trial demonstrates the feasibility of QST in depressive patients.

Right-lateralized pain processing in the human cortex: an FMRI study

Neuroimaging studies of human pain have revealed a widespread "pain matrix" distributed across both hemispheres of the brain. It is not resolved whether the pain matrix is biased toward one hemisphere, although behavioral and clinical data suggest that pain is perceived differently on the two sides of the body, and several neuroimaging studies suggest that pain processing in some regions of cortex may be lateralized toward the right hemisphere. The current study used fMRI in nine subjects to determine whether acute pain is preferentially processed in one cortical hemisphere. All cortical areas that were activated during the painful simulation were investigated, and several analytic approaches were used to directly compare activated regions to similar regions in the opposite hemisphere. Results indicated that four regions of the cortical pain matrix were activated either contralaterally (somatosensory cortex) or bilaterally (mid/posterior insula, anterior insula, and posterior cingulate). In addition, activation in five cortical regions during acute pain stimulation was localized either exclusively in the right hemisphere or was strongly lateralized to the right. These five areas were in the middle frontal gyrus, anterior cingulate, inferior frontal gyrus, medial/superior frontal gyri, and inferior parietal lobule. The location of some of these regions is consistent with the idea that there may be a right-lateralized attentional system to alert an organism to an infrequent, but behaviorally relevant, stimulus such as pain.

Pain perception in major depression depends on pain modality

One frequently described feature of depression is an increased vulnerability to pain complaints, and chronic pain is frequently accompanied by symptoms of depression. In contrast to this, a decreased sensitivity to experimental pain has been described in major depression. The physiological basis of this phenomenon is yet elusive. We investigated 30 patients suffering from a major depressive disorder and matched controls. Pain testing (threshold and tolerance) was performed on both sides of the body and included assessment of thermal, electrical and ischemic pain. While confirming hypoalgesia to heat and electrical pain in comparison to controls, we found hyperalgesia to ischemic muscle pain. Furthermore, thermal pain tolerance and electrical pain tolerance were significantly increased on the right hand side confirming previous results of a lateralized perception of pain in depression. Our main finding suggests that painful stimuli are processed differentially depending on the localization of pain induction in depression. This knowledge may enable us to understand and ultimately treat pain complaints more appropriately in depressed patients.

Impairment of pain inhibition in chronic tension-type headache

Evidence has been accumulated suggesting that a dysfunction in pain inhibitory systems, i.e. in 'diffuse noxious inhibitory controls' (DNIC)-like mechanisms, might be-amongst other factors-responsible for the development of anatomically generalized chronic pain like fibromyalgia. The aim of the present study was to look for similar impairments in chronic tension-type headache (CTTH) as a regionally specific pain syndrome. Twenty-nine CTTH patients and 25 age- and sex-matched healthy control subjects participated in the study. After baseline assessment of electrical detection and pain thresholds, tonic heat stimuli were concurrently applied by a thermode to the thigh to induce DNIC-like pain inhibition. Tonic heat stimuli were applied either slightly above ('pain' condition) or slightly below ('heat' condition) pain threshold. For determination of electrical detection and pain thresholds, electrocutaneous stimuli were administered either to the forearm (extra-cranial site) or to the temple (cranial site), using a multiple staircase procedure. The increase in the electrical detection and pain thresholds induced by concurrent tonic heat stimulation was significantly smaller in the CTTH patients than in the control subjects. This group difference was present during the 'pain' as well as the 'heat' condition. Furthermore, the electrical detection and pain thresholds were affected in this group-specific manner both at the forearm and at the temple. These findings suggest that patients with CTTH suffer from deficient DNIC-like pain inhibitory mechanisms in a similar manner, as do patients with anatomically generalized chronic pain like fibromyalgia.

Decreased sensitivity to experimental pain in adjustment disorder

An altered perception of pain has been described for several psychiatric disorders. To date the influence of adjustment disorders (AD) on pain perception has not been described. Here, we investigated perception of experimentally induced pain in 15 patients suffering from AD (subtype with depressive symptoms) and controls matched for age and sex. Thresholds and tolerances were assessed for thermal and electrical pain on both sides of the body. We found an overall increase of pain thresholds and tolerances in AD patients as compared to controls, predominately on the right side of the body. Analogue findings have been reported for pain perception in major depressive disorder (MDD). Of the data obtained, only thermal pain threshold on the right arm correlated with the severity of depressive symptoms. Although the underlying pathology is elusive it is likely that the mechanisms for reduced pain sensitivity are comparable in MDD and AD.

Deep pain thresholds in the distal limbs of healthy human subjects

Pressure pain thresholds (PPTs) in distal limbs have been under-investigated despite their potential clinical importance. Therefore, we compared PPTs over nail bed, bony prominences, and muscle in distal parts of upper and lower limbs. We investigated 12 healthy subjects using three handheld devices: a spring-loaded, analogue pressure threshold meter (PTM) with two operating ranges, and an electronic Algometer. PPTs were determined with three series of ascending stimulus intensities with a ramp of about 50 kPa/s. PPTs were normally distributed in logarithmic space. PPTs over different tissues varied significantly (ANOVA, p<0.001): mean thresholds and 95% confidence intervals were 615 kPa (266-1424 kPa) over the nail bed, 581 kPa (271-1245 kPa) over bony prominences, and 520 kPa (246-1100 kPa) over muscles. PPTs on the foot were higher than on the hand (ANOVA, p<0.01), except over muscles. PPTs were significantly lower with the Algometer than with PTMs (ANOVA, p<0.01); again these differences were least when testing over muscle. There was no significant right-left difference (ANOVA, p=0.33). In spite of considerable variability across subjects, reproducibility within subjects was high (correlation coefficients>0.90). For within-subject comparisons, threshold elevations beyond 33-43% would be abnormal (95% confidence intervals), whereas only deviations from the group mean by at least a factor of two would be abnormal with respect to absolute normative values. PPTs over distal muscles were comparable to published values on proximal limb and trunk muscles. These findings suggest that pressure pain testing over distal muscles may be a sensitive test for deep pain sensitivity and that the simple and less expensive devices are sufficient for testing this tissue type. Intra-individual site-to-site comparisons will be more sensitive than absolute normative values.