Neuropathic pain assessment: update on laboratory diagnostic tools

Corneal Neuropathic Pain: A Patient and Physician Perspective

Corneal neuropathic pain (CNP) is a debilitating condition characterized by pain in the absence of a noxious stimulus. Symptoms such as ocular stinging, burning, photophobia, irritation, and a deep aching pain can be severe despite a seemingly normal ocular surface on examination. CNP may develop due to either peripheral or central sensitization. Peripheral sensitization develops due to aberrant regeneration of corneal nociceptors and nerve fibers as a result of corneal injury or disease of peripheral corneal nerves. Whereas, central sensitization develops due to upregulation of excitatory neurotransmitters as a result of chronic inflammation, which leads to amplification of neuronal response to stimuli. Unfortunately, due to the disparity in severity of symptomology and the observable signs on examination, patients' symptoms are commonly thought to be "psychological" or "functional", and patients report feeling ignored and neglected. Additionally, diagnosis is often delayed which adversely affects patient outcomes. Research to date has focused on the scientific aspects of corneal neuropathic pain: its pathophysiology, epidemiology, investigations, and management. Research into the patient personal experience and the challenges faced by individual patients and their clinicians is lacking. We present the patient and physician perspective on the journey of both patients in order to provide insights into the challenges faced by patients and physicians in the diagnosis, assessment, and management of corneal neuropathic pain.

Pain during the first year after scoliosis surgery in adolescents, an exploratory, prospective cohort study

Objective

Approximately 50% of adolescents who have undergone scoliosis surgery still experience severe pain one year postoperatively. We explored the postoperative pain trajectory and the potential value of preoperative Thermal Quantitative Sensory Testing (T-QST) as predictor of chronic postsurgical pain after scoliosis surgery.

Design

Single-center prospective cohort study in adolescents undergoing scoliosis surgery.

Outcomes

Prevalence of chronic postsurgical pain (CPSP) one year after scoliosis surgery and postsurgical pain course during this year. The need for rescue medication and the relationship between pre-operative T-QST, acute pain and CPSP.

Results

Thirty-nine patients (mean age 13.9 years; SD 1.9 years) completed the study. One year postoperatively, ten patients (26%) self-reported pain [numeric rating scale (NRS) score ≥ 4]) when moving and two (5%) when in rest. Four of these patients (10.3%) experienced neuropathic pain. The pre-operative cold pain threshold was lower (p = 0.002) in patients with CPSP at 12 months. Preoperative cold and heat pain thresholds were correlated with the number of moderate or severe pain reports (NRS ≥ 4) in the first week postoperatively (r -.426; p = 0.009 and r.392; p = 0.016, respectively).

Conclusions

One year after scoliosis surgery, a significant part of patients (26%) still reported pain, some with neuropathic characteristics. Better diagnosis and treatment is needed; our study suggests that T-QST could be further explored to better understand and treat children with this negative outcome.

A review of nutrition in neuropathic pain of leprosy

Leprosy is a neglected tropical disease (NTD) that continues to burden low- and middle-income countries (LMICs), despite being eliminated as a public health concern by the World Health Organization (WHO) in 2000. The causative agents, Mycobacterium leprae and Mycobacterium lepromatosis, affect nearly 200,000 individuals globally each year, with over 19,000 new cases detected in the Americas in 2020 alone. Canada has experienced an increasing incidence of leprosy, due to rising levels of travel and migration from endemic areas, reaching over 37,000 individuals with leprosy by the end of 2020. Patients experience a spectrum of signs and symptoms including hypopigmented cutaneous macules alongside peripheral neuropathy including peripheral neuropathic pain (PNP) and disabling sensory neuropathies. Despite the development of effective and curative therapeutics via multidrug therapy (MDT), many barriers to treatment adherence and effective immunological control of the pathogen challenge the care of patients with leprosy. Socioeconomic barriers, such as disability-related social stigma and often undiagnosed nutritional deficiencies, have resulted in heightened disease severity. PNP therapeutics are associated with significant side effects and remain ineffective as the majority of individuals will not experience a greater than 30% reduction of symptoms. Nutrient supplementation is known to be instrumental in reducing host oxidative stress, strengthening the immune system and mitigating comorbidities. Likewise, dietary lifestyle interventions known to be physiologically beneficial have recently emerged as powerful tools conferring neuroprotective effects, potentially mitigating PNP severity. However, a significant knowledge gap concerning the effect of adequate nutrition on host immunological control of leprosy and PNP severity exists. Further evaluation of this relationship will provide key insight into the pathogenesis of leprosy, strengthening the current body of literature.

Associations of Small Fiber Neuropathy with Geriatric Nutritional Risk Index and Arterial Stiffness in Hemodialysis

BACKGROUND

Peripheral neuropathy is a common neurological complication in uremic patients, and quantitative sensory testing (QST) is effective for diagnosis of small fiber neuropathy. Malnutrition and arterial stiffness are prevalent in patients undergoing hemodialysis (HD). The associations of small fiber neuropathy with nutritional status and arterial stiffness remain uncertain in maintenance HD patients.

METHODS

A total of 152 HD patients were included. Geriatric nutritional risk index (GNRI), an indicator of nutritional status, was calculated by serum albumin and actual and ideal body weight. Arterial stiffness was defined as brachial-ankle pulse wave velocity (baPWV) > 1400 cm/s. Small fiber neuropathy was assessed by an abnormal QST threshold of cold and warm sensation in patients' hands or feet. Multivariate forward logistic regression analysis was performed to examine the associations among abnormal QST threshold, GNRI, and arterial stiffness.

RESULTS

baPWV and prevalence of abnormal QST threshold were significantly higher in diabetic patients. Multivariate logistic analyses revealed that older age (OR, 1.081; 95% CI, 1.026-1.139, p = 0.003) and male gender (OR, 4.450; 95% CI, 1.250-15.836, p = 0.021) were associated with abnormal warm threshold of hands. Furthermore, diabetes (OR, 3.966; 95% CI, 1.351-11.819, p = 0.012) and lower GNRI (per 1 unit increase, OR, 0.935, 95% CI, 0.887-0.985, p = 0.012) were associated with abnormal cold threshold of feet. Arterial stiffness (OR, 5.479, 95% CI, 1.132-22.870, p = 0.020) and higher calcium-phosphorus product (OR, 1.071, 95% CI, 1.013-1.132, p = 0.015) were associated with abnormal warm threshold of feet.

CONCLUSIONS

Lower GNRI and arterial stiffness were significantly associated with small fiber neuropathy in patients undergoing HD. Malnutrition risk and vascular factors might play important roles in small fiber neuropathy among patients undergoing HD.

Current View of Diagnosing Small Fiber Neuropathy

Small fiber neuropathy (SFN) is a disorder of the small myelinated Aδ-fibers and unmyelinated C-fibers [5, 6]. SFN might affect small sensory fibers, autonomic fibers or both, resulting in sensory changes, autonomic dysfunction or combined symptoms [7]. As a consequence, the symptoms are potentially numerous and have a large impact on quality of life [8]. Since diagnostic methods for SFN are numerous and its pathophysiology complex, this extensive review focusses on categorizing all aspects of SFN as disease and its diagnosis. In this review, sensitivity in combination with specificity of different diagnostic methods are described using the areas under the curve. In the end, a diagnostic work-flow is suggested based on different phenotypes of SFN.

Diagnosis and Treatment of Chronic Neuropathic and Mixed Pain in Children and Adolescents: Results of a Survey Study amongst Practitioners

Validated diagnostic tools to diagnose chronic neuropathic and mixed pain in children are missing. Therapeutic options are often derived from therapeutics for adults. To investigate the international practice amongst practitioners for the diagnosis and treatment of chronic, neuropathic pain in children and adolescents, we performed a survey study among members of learned societies or groups whose members are known to treat pediatric pain. The survey included questions concerning practitioners and practice characteristics, assessment and diagnosis, treatment and medication. We analyzed 117 returned questionnaires, of which 41 (35%) were fully completed and 76 (65%) were partially completed. Most respondents based the diagnosis of neuropathic pain on physical examination (68 (58.1%)), patient history (67 (57.3%)), and underlying disease (59 (50.4%)) combined. Gabapentin, amitriptyline, and pregabalin were the first-choice treatments for moderate neuropathic pain. Tramadol, ibuprofen, amitriptyline, and paracetamol were the first-choice treatments for moderate mixed pain. Consensus on the diagnostic process of neuropathic pain in children and adolescents is lacking. Drug treatment varies widely for moderate, severe neuropathic, and mixed pain. Hence, diagnostic tools and therapy need to be harmonized and validated for use in children.

Ocular Surface Alterations in the Context of Corneal In Vivo Confocal Microscopic Characteristics in Patients With Fibromyalgia

PURPOSE

To quantify the morphology of corneal basal epithelium and subbasal nerves and to evaluate the ocular surface alterations in patients with fibromyalgia (FM).

METHODS

Patients with FM (n = 34) and healthy controls (n = 42) were enrolled. All participants underwent ocular surface tests in the following order: corneal sensitivity, tear film breakup time, lissamine green staining, Schirmer test, and the Ocular Surface Disease Index questionnaire. Basal epithelial cells and subbasal nerves were evaluated using in vivo confocal microscopy (IVCM). Demographic characteristics, Visual Analog Scale for Pain (VAS), American College of Rheumatology 1990, the Widespread Pain Index (WPI), and the Symptom Impact Questionnaire (SIQR) scores of patients with FM were obtained.

RESULTS

Corneal sensitivity was 0.4 g/mm (fiber length: 6.0 cm) in all eyes. Patients with FM had a higher Ocular Surface Disease Index (42.2 ± 18.9 vs. 1.2 ± 1.7, P < 0.001), higher lissamine green staining scores (0.5 ± 0.5 vs. 0.05 ± 0.2, P < 0.001), and lower tear breakup time scores (9.0 ± 3.6 vs. 10.3 ± 1.5, P = 0.003) than the controls. Basal epithelial cell density (2709 ± 494 vs. 4491 ± 724), total nerve density (1563 ± 620 vs. 2545 ± 973), long nerve fibers (3.4 ± 1.3 vs. 4.5 ± 1.0), and the number of nerves (5.0 ± 1.8 vs. 10.3 ± 2.1) were all lower in patients with FM compared with those of the controls (P < 0.001 for all). There was a statistically significant negative correlation between the WPI score and Schirmer test results (rho = -0.374, P = 0.03) and between WPI and total nerve density (rho = -0.334, P = 0.054).

CONCLUSIONS

To the best of our knowledge, this is the first study that evaluated ocular surface alterations in the context of corneal IVCM characteristics. Patients with FM should be evaluated in terms of ocular surface diseases. IVCM may be used in FM to assess small fiber neuropathy.

Microglial role in the development of chronic pain

PURPOSE OF REVIEW

The review aims to present the latest research into microglia and their role in pain.

RECENT FINDINGS

Microglia affect sex and age-dependent differences in pain. The various microglial phenotypes make their involvement in pain more complex but provide more potential as pain modulators.

SUMMARY

Glial cells, composed of microglia, astrocytes, and oligodendrocytes, outnumber neurons in the central nervous system. The crosstalk between these cells and neurons is now established as participating in the development of chronic pain. There has been a great advance in the description of microglia reactivity from pro to anti-inflammatory phenotypes. The modulation of these phenotypes could be a potential target for pain therapy. Recently, different microglial reactivity between man and woman and between neonates and adults, in response to nerve injury were described, which could explain some of the sex differences in pain sensitivity and the absence of neuropathic pain development in neonates. Clinical trials using microglia as a target have been carried out in various neurological diseases and pain, with limited efficacy in the latter, but there are nonetheless, indications that with some improvement in study strategies microglia could be a future target for pain control.

The research gap in chronic paediatric pain: A systematic review of randomised controlled trials

BACKGROUND AND OBJECTIVE

Chronic pain is associated with significant functional and social impairment. The objective of this review was to assess the characteristics and quality of randomized controlled trials (RCTs) evaluating pain management interventions in children and adolescents with chronic pain.

METHODS

We performed a systematic search of PubMed, Embase and the Cochrane Library up to July 2017. We included RCTs that involved children and adolescents (3 months-18 years) and evaluated the use of pharmacological or non-pharmacological intervention(s) in the context of pain persisting or re-occurring for more than 3 months. Methodological quality was evaluated using the Cochrane Risk of Bias (ROB) Tool.

RESULTS

A total of 58 RCTs were identified and numbers steadily increased over time. The majority were conducted in single hospital institutions, with no information on study funding. Median sample size was 47.5 participants (Q1,Q3: 32, 70). Forty-five percent of RCTs included both adults and children and the median of the mean ages at inclusion was 12.9 years (Q1,Q3: 11, 15). Testing of non-pharmacological interventions was predominant and only 5 RCTs evaluated analgesics or co-analgesics. Abdominal pain, headache/migraine and musculoskeletal pain were the most common types of chronic pain among participants. Methodological quality was poor with 90% of RCTs presenting a high or unclear ROB.

CONCLUSIONS

Evaluation of analgesics targeting chronic pain relief in children and adolescents through RCTs is marginal. Infants and children with long-lasting painful conditions are insufficiently represented in RCTs. We discuss possible research constraints and challenges as well as methodologies to circumvent them.

SIGNIFICANCE

There is a substantial research gap regarding analgesic interventions for children and adolescents with chronic pain. Most clinical trials in the field focus on the evaluation of non-pharmacological interventions and are of low methodological quality. There is also a specific lack of trials involving infants and children and adolescents with long-lasting diseases.

A Protocol of Manual Tests to Measure Sensation and Pain in Humans

Numerous qualitative and quantitative techniques can be used to test sensory nerves and pain in both research and clinical settings. The current study demonstrates a quantitative sensory testing protocol using techniques to measure tactile sensation and pain threshold for pressure and heat using portable and easily accessed equipment. These techniques and equipment are ideal for new laboratories and clinics where cost is a concern or a limiting factor. We demonstrate measurement techniques for the following: cutaneous mechanical sensitivity on the arms and legs (von-Frey filaments), radiant and contact heat sensitivity (with both threshold and qualitative assessments using the Visual Analog Scale (VAS)), and mechanical pressure sensitivity (algometer, with both threshold and the VAS). The techniques and equipment described and demonstrated here can be easily purchased, stored, and transported by most clinics and research laboratories around the world. A limitation of this approach is a lack of automation or computer control. Thus, these processes can be more labor intensive in terms of personnel training and data recording than the more sophisticated equipment. We provide a set of reliability data for the demonstrated techniques. From our description, a new laboratory should be able to set up and run these tests and to develop their own internal reliability data.

Somatosensory deficits after stroke: a scoping review

In the past years, there have been increasing research activities focusing on somatosensory symptoms following stroke. However, as compared to the large number of clinical and neuroimaging studies on motor symptoms, the number of studies tracing somatosensory symptoms after stroke and their recovery is rather small. It is an ongoing discussion, to which extent somatosensory deficits after stroke influence patient's long-term outcome in motor and sensory performance and functional independence in activities of daily living. Modern brain imaging techniques allow for studying the impact of stroke lesion localization and size on acute and persisting clinical impairment. Here, we review the literature on somatosensory symptoms after stroke. We summarize epidemiological information on frequency and characteristics of somatosensory symptoms affecting all parts of the body in the acute and chronic stage of stroke. We further give an overview of brain imaging studies of stroke affecting the somatosensory system. Finally, we identify open questions which need to be addressed in future research and summarize the implications for clinical practice.

Challenges in the diagnosis and treatment of neurosarcoidosis

The diagnosis and treatment of neurosarcoidosis can be very challenging for several reasons. It affects clinically 5%-10% of sarcoidosis patients, but can be found in up to 25% of autopsies. These data reveal that a high percentage of asymptomatic or misdiagnosed cases can be missed at an initial diagnostic approach. Clinical and imaging findings are often non-specific since they can be found in a large number of neurological disorders. Histopathology can also be confounding if not performed by an expert pathologist and not placed in an appropriate clinical context. In this review, we discuss clinical features, laboratory findings, imaging, and histology of neurosarcoidosis, and we report current evidence regarding drug therapy. We conclude that a correct diagnostic approach should include a multidisciplinary evaluation involving clinicians, radiologists, and pathologists and that future studies should evaluate the genetic signature of neurosarcoidosis as they could be helpful in the assessment of this uncommon disease. With head-to-head comparisons of medical treatment for neurosarcoidosis still lacking due to the rarity of the disease and an increasing number of immunomodulating therapies at hand, novel therapeutic approaches are to be expected within the next few years.