Gain-of-function mutations in , which encodes the Nav1.7 voltage-gated sodium channel, are known to cause primary erythromelalgia (PEM). This condition is characterized by recurrent episodes of erythema, burning pain, and warmth in the extremities. These genetic insights have spurred the development of Nav1.7 blockers as a promising therapeutic strategy for PEM. However, translating these findings into effective clinical treatments has remained challenging. In this study, we demonstrate that mepyramine, a compound previously shown to alleviate pain in animal models, effectively targets hNav1.7 channels carrying PEM-associated gain-of-function mutations, providing substantial pain relief in PEM patients. Using voltage-clamp recordings in human embryonic kidney (HEK) 293 cells, we demonstrated that mepyramine inhibits hNav1.7 channels carrying three distinct PEM mutations, I848T, L858F, and L1267V, which differentially affect the gating properties of hNav1.7. Importantly, mepyramine's efficacy was consistent regardless of how these mutations altered channel activation or inactivation properties. To evaluate its clinical potential, we administered a high-dose topical formulation of mepyramine to a group of PEM patients suffering from severe pain that was unresponsive to conventional analgesics, including cases with identified mutations. This treatment rapidly and durably reduced burning pain and erythema, providing meaningful relief for patients who had not responded to, or could not tolerate, previous therapies. These results suggest that mepyramine can inhibit PEM-associated Nav1.7 channel mutants and may offer a new therapeutic approach for PEM patients.
To assess the contribution of large and small nerve fiber alteration in erythromelalgia (EM). Thirty-three EM patients were included and underwent clinical evaluation based on EM severity score, DN4, and Utah Early Neuropathy Scale (UENS) score. Neurophysiological evaluation consisted in nerve conduction studies (NCS) for large nerve fibers and specific tests for small nerve fibers: electrochemical skin conductance, cold and warm detection thresholds, and laser evoked potentials. Finally, the evaluation of vascular changes was based on the presence of clinical feature of microvascular disorders and the measurement of the Toe Pressure Index (TPI). While 28 patients (85%) had vascular alteration on TPI or clinical features, 23 patients (70%) had small-fiber neuropathy on neurophysiological tests, and only 10 patients (30%) had large fiber neuropathy on NCS. Regarding clinical scores, there was no difference between groups (presence or absence of large- or small-fiber neuropathy or microvascular disorder) except for a higher UENS score in patients with large fiber neuropathy. Peripheral neuropathy, mostly involving small nerve fibers, is almost as common as microvascular changes in EM, but remains inconstant and not related to a specific neuropathic pattern or higher clinical severity. The association of neuropathic and vascular factors is not systematic in EM, this syndrome being characterized by different pathophysiological mechanisms leading to a common clinical phenotype.
Several pharmacological treatments are recommended for Raynaud's phenomenon (RP) secondary to systemic sclerosis, but they only have modest efficacy. A way to efficiently identify new drugs is drug repurposing, which can be based on signature matching. The signature could be derived from chemical structures, pharmacological affinity or adverse event profiles. We propose to use the World Health Organization (WHO) pharmacovigilance database to generate repositioning hypotheses for treatments of RP through adverse event signature matching. We first screened all drugs associated with at least 1 case of erythromelalgia, an adverse effect opposite to RP. In parallel, to define the adverse event signature of drugs recommended in secondary RP from the WHO pharmacovigilance database, we selected the 14 most representative adverse drug reactions (ADRs). Lastly, we performed a hierarchical cluster analysis to identify drugs with similar ADR signature to vasodilatory drugs used in RP. In total, 179 drugs were associated with erythromelalgia; they were related to 860 334 adverse events representative of RP drugs in the WHO pharmacovigilance database. Hierarchical cluster analysis allowed identification of 6 clusters. The most stable cluster contained 7 drugs, among which 5 are recommended in secondary RP, or pertain to the same drug class: epoprostenol, nifedipine, nicardipine, lacidipine and israpidine. The 2 remaining drugs were alemtuzumab and fumaric acid. Our ADR signature matching approach suggests that alemtuzumab and fumaric acid could be effective treatments of secondary RP. The latter is currently being investigated as a treatment of pulmonary hypertension in systemic sclerosis.
Olmsted syndrome is a genodermatosis characterized by painful and mutilating palmoplantar keratoderma (PPK) that progresses from infancy onward and lacks an effective treatment. It is most often caused by mutations in the transient receptor potential vanilloid 3 (TRPV3) gene. In animal models and keratinocyte cell lines, TRPV3 signaling leads to epidermal growth factor receptor (EGFR) transactivation. To examine the possibility of blocking EGFR transactivation with the inhibitor erlotinib hydrochloride to treat PPK in patients with Olmsted syndrome due to TRPV3 mutations. In this case series, 3 patients from 2 unrelated families who had TRPV3-mutation-associated PPK were treated with erlotinib from May 5, 2018, through May 13, 2019. Clinical follow-up included evaluation of PPK progression, pain and interventions for pain, as well as erlotinib dose adjustment based on treatment effect, plasma levels, and tolerance. The 3 patients (2 brothers aged 15 and 17 years and a 13-year-old girl) had severe palmoplantar hyperkeratosis, intolerable pain with erythromelalgia, severe growth delay, anorexia, and insomnia, which had been progressing since infancy despite numerous therapies. Two patients were confined to wheelchairs owing to intense pain and joint restrictions because of hyperkeratosis. All patients experienced depression and did not engage in social activities. Within 3 months of initiating therapy with erlotinib, hyperkeratosis and pain disappeared. All patients were able to touch the ground with their feet, wear shoes, and walk. Anorexia and insomnia remitted and paralleled improved growth. In addition, the patients resumed social activities. These improvements were sustained across 12 months of treatment and follow-up. The doses of erlotinib used were lower than those used in oncology, and only mild to moderate adverse effects were noted. The findings of this study report improvement of PPK in patients with Olmsted syndrome caused by TRPV3 mutations when treated with erlotinib. Targeting EGFR transactivation with erlotinib therapy may result in clinical remission in an orphan disease that lacks an effective intervention.
Fabry disease is a rare X-linked metabolic disorder characterized by a deficiency in the enzyme alpha-galactosidase A. Both males and females can be affected. The main presenting symptom is pain in the extremities, whereas at a more advanced stage, the manifestations include hypertrophic cardiomyopathy, cardiac dysrhythmia, proteinuria, chronic kidney dysfunction, stroke, and hearing loss. When not diagnosed and treated, Fabry disease causes early death. No studies specifically designed to describe the musculoskeletal manifestations of Fabry disease are available. We conducted a single-center retrospective study of patients receiving follow-up at a Fabry disease referral center. We described the musculoskeletal manifestations and analyzed the differential diagnoses. Our study included 40 patients belonging to 20 families, including 25 females with a mean age of 44.2 years (range, 20-76 years) and 15 males with a mean age of 40.1 years (range, 16-61 years). Mean age at the diagnosis of Fabry disease was 37.2 years (range, 7-71 years) in the females and 26.9 years (range, 9-51 years) in the males. Specific enzyme replacement therapy was given to 10 (40%) females and 12 (80%) males. Musculoskeletal manifestations were as follows: past or present pain in the extremities (13 females and 10 males), combined in some patients with vasomotor disorders in the extremities and telangiectasia; exercise intolerance (12 females and 12 males); osteoporotic fractures (2 brothers aged 45 and 44 years, respectively); osteoporosis (3 females, aged 57, 63, and 75 years, respectively), which contributed to death in the oldest patient; osteopenia (2 females aged 38 and 47 years, respectively; and 1 male aged 43 years); Charcot foot and lymphedema with serious infectious complications (4 males older than 40 years), with avascular osteonecrosis of the lower limbs in 2 cases; toe amputations (3 cases); bilateral lower-limb amputation (1 case); abnormally slender lower limbs (5 females and 8 males); acute gout (3 males with severe chronic kidney failure); and carpal tunnel syndrome (1 female and 1 male, both younger than 40 years). Mistaken diagnoses that were made at an early stage, contributing to delay the identification of Fabry disease, included rheumatic fever (2 females and 2 males), growing pains (2 males), pain with paralysis (1 female), chilblains of the lower limbs (1 female), and erythermalgia (1 female). In adulthood, the following mistaken diagnoses were made: Sjögren's syndrome and/or sicca syndrome (6 females), systemic sclerosis (1 male), dysautonomia (1 female), and familial Mediterranean fever (1 female). The diagnosis of Fabry disease is usually delayed, due to confusion with more common disorders. Musculoskeletal manifestations may constitute the presenting symptoms. Past or present pain in the extremities is typical. Osteoporosis may develop early and become severe. Together with the family history, the presence of musculoskeletal manifestations can lead to the correct diagnosis by prompting alpha-galactosidase assays in males and genetic testing in females. Fabry disease is often responsible for musculoskeletal manifestations, of which the most common are pain in the extremities and osteoporosis. These manifestations can be inaugural and lead to diagnostic wanderings. They require specific treatment strategies.
Olmsted syndrome (OS) is a rare keratinizing disorder characterized by excessive epidermal thickening of the palms and soles, with clinical and genetic heterogeneity. Approximately 50 cases have been reported, with the molecular basis described in only 9. Recently, TRPV3 (transient receptor potential vanilloid 3) mutations were identified in autosomal-dominant OS in 7 sporadic cases and 1 familial case, whereas an MBTPS2 (membrane-bound transcription factor protease, site 2) mutation was reported in X-linked recessive OS. We report a new sporadic case of severe, atypical OS and its underlying genetic basis. Our patient is a young girl with severe nonmutilating (palmo)plantar keratoderma without periorificial keratotic plaques associated with intense acute flares of inflammation, itching, burning pain, vasodilatation, and redness of the extremities consistent with erythromelalgia. Whole exome sequencing of patient DNA identified a novel de novo heterozygous missense mutation within TRPV3, p.Leu673Phe, predicted to be damaging. This case study further implicates TRPV3 in OS pathogenesis. In addition, previous reports of OS have not described erythromelalgia as a clinical feature. Its occurrence in our patient could be a chance event, but, if associated with OS, the features of erythromelalgia may expand the phenotypic spectrum of this rare syndrome.
Chronic pain is usually underestimated in children, due to lack of knowledge and its specific signs. In addition to suffering, chronic pain causes a physical, psychological, emotional, social, and financial burden for the child and his family. Practitioners may find themselves in a situation of failure with depletion of medical resources. Some types of chronic pain are refractory to conventional systemic treatment and may require the use of regional anesthesia. Cancer pain is common in children and its medical management is sometimes insufficient. It is accessible to neuroaxial or peripheral techniques of regional anesthesia if it is limited to an area accessible to one of these techniques and no contraindications (e.g., thrombopenia) are present. Complex regional pain syndrome 1 is not rare in children and adolescents, but it often goes undiagnosed. Regional anesthesia may contribute to the treatment of complex regional pain syndrome 1, mainly in case of recurrence, because it provides rapid effective analgesia and allows rapid implementation of intensive physiotherapy. These techniques have also shown interest in phantom limb pain after limb amputation, but they remain controversial for erythromelalgia pain or chronic abdominopelvic pain. Finally, the treatment of postdural puncture headache due to cerebrospinal fluid leak can be treated by performing an epidural injection of the patient's blood, called a blood-patch. Finally, the management of children with chronic pain should be multidisciplinary (pediatrician, physiotherapist, psychologist, surgeon, anesthesiologist) to support the child and her problem in its entirety.
Congenital insensitivity to pain (CIP) is a rare syndrome with various clinical expressions, characterized by a dramatic impairment of pain perception since birth. In the 1980s, progress in nerve histopathology allowed to demonstrate that CIP was almost always a manifestation of hereditary sensory and autonomic neuropathies (HSAN) involving the small-calibre (A-delta and C) nerve fibres which normally transmit nociceptive inputs along sensory nerves. Identification of the genetic basis of several clinical subtypes has led to a better understanding of the mechanisms involved, emphasizing in particular the crucial role of nerve growth factor (NGF) in the development and survival of nociceptors. Recently, mutations of the gene coding for the sodium channel Nav1.7--a voltage-dependent sodium channel expressed preferentially on peripheral nociceptors and sympathetic ganglia--have been found to be the cause of CIP in patients showing a normal nerve biopsy. This radical impairment of nociception mirrors the hereditary pain syndromes associated with "gain of function" mutations of the same ion channel, such as familial erythromelalgia and paroxysmal extreme pain disorder. Future research with CIP patients may identify other proteins specifically involved in nociception, which might represent potential targets for chronic pain treatment. Moreover, this rare clinical syndrome offers the opportunity to address interesting neuropsychological issues, such as the role of pain experience in the construction of body image and in the empathic representation of others' pain.