Pain paths among post-COVID-19 condition subjects: A prospective cross-sectional study with in-person evaluation.

BACKGROUND: New-onset chronic pain has been acknowledged as part of the post-COVID-19 condition. However, available fine-grained data about its clinical phenotype, trajectories and main associated characteristics remain scarce. We described the distinct temporal evolutions of post-COVID-19 pain and their epidemiological and phenotypical features. METHODS: A prospective cross-sectional study enrolled post-COVID-19 condition patients (i.e. who had persisting COVID-19-related symptoms over 30 days since their first positive laboratory test), whose COVID-19 diagnosis had been supported by RT-PCR of oral/nasopharyngeal swab or serology. They underwent in-person evaluations with a structured interview, pain and quality-of-life-related questionnaires and thorough physical examination. Chronic pain (CP) and probable neuropathic pain (NP) were defined according to IASP criteria. RESULTS: The present study included 226 individuals, 177 (78.3%) of whom presented over 3 months since their first COVID-19 symptom. New-onset pain occurred in 170 (75.2%) participants and was chronic in 116 (68.2%). A chronic course was associated with COVID-19-related hospitalization, new-onset fatigue, lower cognitive performance, motor and thermal sensory deficits, mood and sleep impairments and overall lower quality-of-life levels. Probable NP occurred in only 7.6% new-onset pain patients, and was associated with pain chronification, new-onset fatigue, motor and thermal sensory deficits, mechanical allodynia and lower rates of SARS-CoV-2 vaccination. Previous CP was reported by 86 (38.1%) individuals and had aggravated after the infection in 66 (76.7%) of them, which was associated with orthostatic hypotension. CONCLUSIONS: Post-COVID pain phenomena follow different paths, which are associated with specific clinical and epidemiological features, and possibly distinct underlying mechanisms, prognostic and therapeutic implications. SIGNIFICANCE: COVID-19-related pain usually follows a chronic course and is non-neuropathic. Its possible courses and phenotypes are associated with distinct clinical and epidemiological features. This suggests differing underlying mechanisms, which may have significant prognostic and therapeutic implications.

Mirror peripheral neuropathy and unilateral chronic neuropathic pain: insights from asymmetric neurological patterns in leprosy.

ABSTRACT: Leprosy-related multiple mononeuropathy offers a pattern of impairment where neuropathy with and without neuropathic pain (NeP) are present in the same individual, thus allowing to investigate peripheral sensory and innervation in both conditions. This cross-sectional study collected data on clinical and neurological examination, pain assessment questionnaires, quantitative sensory test, and intraepidermal nerve fiber density of patients with leprosy and divided the cohort into 2 groups: with NeP (P+) and without NeP (P-). Furthermore, we assessed mirror body areas in the same NeP individuals with bilateral neuropathy also presenting unilateral NeP. Pain-free patients having unilateral neuropathy were controls. A total of 37 P+ and 22 P- patients were evaluated. Limb areas with NeP had signs of C-fiber dysfunction and hyperesthesia on quantitative sensory testing compared with limb areas having neuropathy without NeP. Skin denervation was found in all patients with leprosy. Comparisons of limbs with and without neuropathy and with and without NeP revealed that higher heat pain thresholds (HPTs) were associated with neuropathic pain areas, whereas less altered HPT was correlated with higher fiber density. Furthermore, a relationship was found between time of leprosy treatment termination and more intense neuropathy, expressed by HPT increasing 0.03°C each month. As expected, interindividual comparisons failed to show differences in intraepidermal nerve fiber density and subepidermal plexus areas between P+ and P- patients ( P = 0.2980, P = 0.9044; respectively). Higher HPT and lower mechanical detection threshold were related to NeP. This study pointed out the relevance of intraindividual comparisons including mirror areas when assessing local changes in peripheral NeP.

Electrical stimulation of the posterior insula induces mechanical analgesia in a rodent model of neuropathic pain by modulating GABAergic signaling and activity in the pain circuitry.

The insula has emerged as a critical target for electrical stimulation since it influences pathological pain states. We investigated the effects of repetitive electrical stimulation of the insular cortex (ESI) on mechanical nociception, and general locomotor activity in rats subjected to chronic constriction injury (CCI) of the sciatic nerve. We also studied neuroplastic changes in central pain areas and the involvement of GABAergic signaling on ESI effects. CCI rats had electrodes implanted in the left agranular posterior insular cortex (pIC), and mechanical sensitivity was evaluated before and after one or five daily consecutive ESIs (15 min each, 60 Hz, 210 µs, 1 V). Five ESIs (repetitive ESI) induced sustained mechanical antinociception from the first to the last behavioral assessment without interfering with locomotor activity. A marked increase in Fos immunoreactivity in pIC and a decrease in the anterior and mid-cingulate cortex, periaqueductal gray and hippocampus were noticed after five ESIs. The intrathecal administration of the GABAA receptor antagonist bicuculline methiodide reversed the stimulation-induced antinociception after five ESIs. ESI increased GAD65 levels in pIC but did not interfere with GABA, glutamate or glycine levels. No changes in GFAP immunoreactivity were found in this work. Altogether, the results indicate the efficacy of repetitive ESI for the treatment of experimental neuropathic pain and suggest a potential influence of pIC in regulating pain pathways partially through modulating GABAergic signaling.

Effects of cerebellar transcranial magnetic stimulation on ataxias: A randomized trial.

INTRODUCTION: Cerebellar ataxia remains a neurological symptom orphan of treatment interventions, despite being prevalent and incapacitating. We aimed to study, in a double-blind design, whether cerebellar modulation could improve ataxia. METHODS: We included patients with diagnosis of spinocerebellar ataxia type 3, multiple systems atrophy cerebellar type, or post-lesion ataxia. Patients received five sessions each of sham and active cerebellar 1 Hz deep repetitive transcranial magnetic stimulation in randomized order. Our primary outcome was the decrease in the Scale for the Assessment and Rating of Ataxia when comparing phases (active x sham). Secondary outcomes measures included the International Cooperative Ataxia Rating Scale, and other motor, cognitive, and quality of life scales. This study was registered at clinicaltrials.gov (protocol NCT03213106). RESULTS: Twenty-four patients aged 29-74 years were included in our trial. After active stimulation, the Scale for the Assessment and Rating of Ataxia score was significantly lower than the score after sham stimulation [median (interquartile range) of 10.2 (6.2, 16.2) versus 12.8 (9.6, 17.8); p = 0.002]. The International Cooperative Ataxia Rating Scale score also improved after active stimulation versus sham [median (interquartile range) of 29.0 (21.0, 43.5) versus 32.8 (22.0, 47.0); p = 0.005]. Other secondary outcomes were not significantly modified by stimulation. No patient presented severe side effects, and nine presented mild and self-limited symptoms. CONCLUSIONS: Our protocol was safe and well-tolerated. These findings suggest that cerebellar modulation may improve ataxic symptom and provide reassurance about safety for clinical practice.

Antinociception induced by motor cortex stimulation: somatotopy of behavioral response and profile of neuronal activation.

Motor cortex stimulation (MCS) is used as a therapy for patients with refractory neuropathic pain. Experimental evidence suggests that the motor cortex (MC) is involved in the modulation of normal nociceptive response, but the underlying mechanisms have not been clarified yet. In previous studies, we demonstrated that MCS increases the nociceptive threshold of naive conscious rats by inhibiting thalamic sensory neurons and disinhibiting the neurons in periaqueductal gray (PAG), with the involvement of the opioid system. The aim of this study was to investigate the possible somatotopy of the motor cortex on MCS-induced antinociception and the pattern of neuronal activation evaluated by Fos and Egr-1 immunolabel in an attempt to better understand the relation between MC and analgesia. Rats received epidural electrode implants placed over the MC, in three distinct areas (forelimb, hindlimb or tail), according to a functional mapping established in previous studies. Nociceptive threshold was evaluated under 15-min electrical stimulating sessions. MCS induced selective antinociception in the limb related to the stimulated cortex, with no changes in other evaluated areas. MCS decreased Fos immunoreactivity (Fos-IR) in the superficial layers of the dorsal horn of the spinal cord for all evaluated groups and increased Fos-IR in the PAG, although no changes were observed in the PAG for the tail group. Egr-1 results were similar to those obtained for Fos. Data shown herein demonstrate that MCS elicits a substantial and selective antinociceptive effect, which is mediated, at least in part, by the activation of descendent inhibitory pain pathway.

Translation to Portuguese and validation of the Douleur Neuropathique 4 questionnaire.

UNLABELLED: The Douleur Neuropathique 4 (DN4) questionnaire was developed by the French Neuropathic Pain Group and is a simple and objective tool, with the ability to distinguish nociceptive from neuropathic pain. The purpose of this work was to validate the DN4 questionnaire in the Portuguese language in order to allow its use in clinical and research settings. A double-blind, accuracy study was conducted, consisting of translation, back-translation, literal evaluation, semantic equivalence, and communication with the target population. The Portuguese version of the questionnaire was applied in a sample of 101 patients with neuropathic (N = 42) or nociceptive pain (N = 59), ranked according to medical diagnosis. The reproducibility, reliability and validity of the instrument were analyzed, and showed a high diagnostic power for this version of the DN4 questionnaire. The Portuguese version of the DN4 questionnaire presented good validity and reliability, allowing it to identify neuropathic pain and neuropathic characteristics of mixed pain syndromes. PERSPECTIVE: This article presents the first validated neuropathic pain questionnaire in the Portuguese language and represents a useful tool in the assessment of neuropathic pain both in the clinical setting and in population-based studies. The sensible and quick format of this instrument are key factors that will contribute to its widespread use, permitting a true recognition of patients with neuropathic pain.