Dissipation of body heat, essential to human life, is largely achieved through sweating. If sweating does not occur normally-as in patients with hypohidrosis (reduced sweating) or anhidrosis (lack of sweating)-the ability to dissipate heat via evaporative mechanisms is overwhelmed. Body temperature may rise, leading to heat-related illness, including heat intolerance, hyperthermia, heat exhaustion, heat stroke, and even death. In patients seen by a dermatologist, anhidrosis may underly and contribute to their symptoms and signs but may be difficult to detect given a limited availability of tools to measure anhidrosis. An association between anhidrosis and skin symptoms including flushing syndromes (eg, facial flushing and erythromelalgia) and widespread skin symptoms (eg, itching, burning, numbness, or tingling, and paresthesias) has recently been described. This review explores the existing dermatologic literature on anhidrosis including clues to the pathophysiology of these disorders, its relationship to skin diseases and symptoms, the tests currently available, and approaches to management. Recognition of an underlying anhidrosis by dermatologists may be important for providing optimal management for patients with heat-related symptoms.

Background and aim COVID-19 mRNA vaccines were granted Emergency Use Authorization by the United States FDA in December 2020. Serious adverse events following immunization (AEFI) with COVID-19 vaccines started to be seen by clinicians soon after the vaccines were available to the public. The objective of this study is to report the clinical course of patients with adverse events following COVID-19 vaccination encountered in medical practice. Methods These cases (age range, 18-82 years) were prospectively identified and collected by the authors during formal or informal consultation from January to December 2021. Cases were excluded from further consideration for AEFI with COVID-19 vaccines if an alternative explanation was deemed more likely at the time of consultation. The authors did not solicit medical providers, patients, or the public, nor screen medical records for adverse events following COVID-19 vaccination. This is a descriptive case series; therefore, no statistical analysis was performed. Results We encountered 18 patients with AEFI, nine (50%) males (range, 22-78 years) and nine (50%) females (range, 18-82 years). Clinical presentations involved various organ systems, including cardiovascular (five), nervous system (five), immune system/hematologic (four), skin (one), gastrointestinal (one), pulmonary (one), and infection (two). This paper details their clinical courses. Conclusions We encountered a variety of AEFI, including myocarditis, demyelinating disease, encephalitis, Bell's palsy, burning mouth syndrome, multisystem inflammatory syndrome, immune thrombocytopenia, pneumonitis, colitis, staphylococcal infection, and erythromelalgia. This detailed case series was presented to help clinicians consider a diagnosis of AEFI for patients when no other explanation has been found after a thorough diagnostic evaluation. These described adverse events following COVID-19 vaccination do not imply causality. We hope this descriptive case series leads to further case-control studies from healthcare organizations to explore the possible risks, incidence, and causal relationships of such adverse events following COVID-19 vaccination.

Erythromelalgia (EM) is an uncommon, multifaceted neurovascular pain disorder. The distal extremities are typically affected, with symptoms of overwhelming warmth, burning pain, and erythema. There is a wide range of presentations with varying severities and courses, including occasional flares, intermittent episodes, and chronic debilitating discomfort. In this narrative review, we aim to raise awareness of EM and synthesize the current state of knowledge through exploring pathophysiology, clinical presentation, differential diagnoses, and treatment options for EM.

Thrombocytosis is defined by guidelines as a platelet count of 450 × 103/μL or greater. It most often results from secondary causes and should resolve with treatment of the underlying condition. Primary thrombocytosis in adults is most commonly due to myeloproliferative neoplasms, including essential thrombocythemia. Thrombocytosis may be identified incidentally in asymptomatic patients or when performing blood tests to investigate symptoms or signs that could indicate microvascular conditions (eg, headaches, paresthesia, erythromelalgia), splenomegaly, thrombosis, and hemorrhage, which are presenting features of essential thrombocythemia. A repeat complete blood cell count with differential and peripheral blood smear should be performed to confirm persistent thrombocytosis and assess other blood cell lines for findings suggestive of myeloproliferative neoplasms. Additional testing, including C-reactive protein levels and iron studies with ferritin levels, should be performed based on history and examination findings. If essential thrombocythemia is suspected in patients with persistent thrombocytosis without an identified cause, testing for Janus kinase 2 gene sequence variations should be performed and, if negative, testing for calreticulin and myeloproliferative leukemia gene sequence variations; a bone marrow biopsy should also be performed. The revised International Prognostic Score of Thrombosis for Essential Thrombocythemia should be calculated to stratify thrombosis risk and guide management, including when to use low-dose aspirin and cytoreductive therapy. Cardiovascular risk factors should also be addressed. Hydroxyurea is the first-line agent in cytoreductive therapy. No treatments have been shown to increase survival or prevent progression to myelofibrosis or leukemia in patients with essential thrombocythemia.

Reflex sympathetic dystrophy (RSD), currently categorized within the spectrum of complex regional pain syndrome (CRPS), is typically considered an acquired disorder characterized by disproportionate pain, erythema, and autonomic changes. In contrast, inherited erythromelalgia is a genetic pain disorder most often caused by gain-of-function variants in SCN9A encoding the Nav1.7 sodium channel and usually presents with bilateral, symmetric distal limb pain and redness. Here, we describe a multigenerational family with a strictly unilateral, trauma-triggered neurovascular pain phenotype associated with a previously unreported heterozygous germline SCN9A variant (c.4784T > G, p. Leu1595Arg). Affected individuals experienced episodic attacks in which minor mechanical or physiological stimuli induced progressive unilateral erythema, warmth, and severe pain spreading from the site of injury and sharply demarcated at the midline, without contralateral involvement. Attacks lasted hours to nearly one day and tended to decrease with age. The variant was absent from population databases and co-segregated with the phenotype within the family, fulfilling ACMG/AMP criteria for likely pathogenicity. The consistent unilateral distribution cannot be explained by mosaicism and is instead compatible with activation of ipsilateral segmental nociceptive and neurovascular reflex circuits that function largely independently across the spinal midline. We propose that excessive positive feedback between C-fiber activation and axon reflex-mediated neurogenic inflammation underlies attack propagation and duration. This framework also suggests therapeutic benefit from agents that interrupt activity-dependent transmitter release, such as gabapentinoids. These findings expand the phenotypic spectrum of SCN9A-related pain disorders and provide a genetically anchored model for unilateral RSD/CRPS-like neurovascular pain.

The article presents a clinical case of secondary erythromelalgia in a comorbid patient with antiphospholipid syndrome, accompanied by burning pain, hyperemia and swelling of the lower extremities. A comprehensive examination involving a neurologist, dermatologist, and rheumatologist was conducted to establish the diagnosis and select the optimal therapy. Significant clinical improvement in the patient's condition is demonstrated against the background of pregabalin therapy. The importance of a multidisciplinary approach and the difficulty of diagnosis due to the lack of specific examination methods and insufficient awareness of doctors about this disease are emphasized. The described case demonstrates the need for a personalized approach to managing patients with erythromelalgia to improve their quality of life.

Thrombocytosis, defined as platelet counts >450 × 10⁹/L, is frequent in the pediatric population and usually secondary to inflammatory conditions or iron deficiency. Essential thrombocythemia (ET), a Philadelphia chromosome-negative myeloproliferative neoplasm, is exceptionally rare in childhood. Pediatric ET often follows an indolent course but carries risks of thrombotic and hemorrhagic events, as well as late progression to myelofibrosis or leukemia. We report the case of a 14-year-old girl presenting with recurrent acral edema, erythema alternating with cyanosis, burning pain, paresthesia, and headaches. Physical examination was unremarkable. Initial suspicion of Raynaud's phenomenon was excluded by nailfold capillaroscopy. Laboratory studies revealed persistent thrombocytosis with platelets over 1,092 × 10⁹/L. Secondary causes were excluded. Bone marrow biopsy revealed megakaryocytic hyperplasia with hyperlobulated megakaryocytes, abdominal ultrasound revealed hepatosplenomegaly, and molecular testing identified a JAK2 V617F mutation, confirming ET. She was initially treated with low-dose acetylsalicylic acid, with partial improvement, but microvascular symptoms persisted, and platelet counts remained >1,000 × 10⁹/L. Hydroxyurea was initiated, leading to progressive platelet reduction and marked clinical benefit. Over three years of follow-up, the patient remained clinically stable, without adverse effects or leukemic transformation. This case illustrates the rarity and diagnostic complexity of pediatric ET, which requires exclusion of reactive causes, bone marrow evaluation, and molecular testing. Management remains particularly challenging due to the absence of pediatric-specific guidelines, with current approaches being largely derived from adult protocols. Cytoreductive therapy may be indicated in cases with extreme thrombocytosis or refractory symptoms, and long-term follow-up is crucial to monitor disease evolution and treatment outcomes. This case highlights the need for multicenter studies and international registries to have pediatric-specific evidence that can better inform diagnostic and therapeutic strategies.