Assessment of cutaneous axon-reflex responses to evaluate functional integrity of autonomic small nerve fibers.

Cutaneous autonomic small nerve fibers encompass unmyelinated C-fibers and thinly myelinated Aδ-fibers, which innervate dermal vessels (vasomotor fibers), sweat glands (sudomotor fibers), and hair follicles (pilomotor fibers). Analysis of their integrity can capture early pathology in autonomic neuropathies such as diabetic autonomic neuropathy or peripheral nerve inflammation due to infectious and autoimmune diseases. Furthermore, intraneural deposition of alpha-synuclein in synucleinopathies such as Parkinson's disease can lead to small fiber damage. Research indicated that detection and quantitative analysis of small fiber pathology might facilitate early diagnosis and initiation of treatment. While autonomic neuropathies show substantial etiopathogenetic heterogeneity, they have in common impaired functional integrity of small nerve fibers. This impairment can be evaluated by quantitative analysis of axonal responses to iontophoretic application of adrenergic or cholinergic agonists to the skin. The axon-reflex can be elicited in cholinergic sudomotor fibers to induce sweating and in cholinergic vasomotor fibers to induce vasodilation. Currently, only few techniques are available to quantify axon-reflex responses, the majority of which is limited by technical demands or lack of validated analysis protocols. Function of vasomotor small fibers can be analyzed using laser Doppler flowmetry, laser Doppler imaging, and laser speckle contrast imaging. Sudomotor function can be assessed using quantitative sudomotor axon-reflex test, silicone imprints, and quantitative direct and indirect testing of sudomotor function. More recent advancements include analysis of piloerection (goose bumps) following stimulation of adrenergic small fibers using pilomotor axon-reflex test. We provide a review of the current literature on axon-reflex tests in cutaneous autonomic small fibers.

Genetic characterization and mutational profiling of foramen magnum meningiomas: a multi-institutional study.

OBJECTIVE: Foramen magnum (FM) meningiomas pose significant surgical challenges and have high morbidity and mortality rates. This study aimed to investigate the distribution of clinically actionable mutations in FM meningiomas and identify clinical characteristics associated with specific mutational profiles. METHODS: The authors conducted targeted next-generation sequencing of 62 FM meningiomas from three international institutions, covering all relevant meningioma genes (AKT1, KLF4, NF2, POLR2A, PIK3CA, SMO, TERT promoter, and TRAF7). Patients with a radiation-induced meningioma or neurofibromatosis type 2 (NF2) were excluded from the study. Additionally, patient and tumor characteristics, including age, sex, radiological features, and tumor location, were retrospectively collected and evaluated. RESULTS: The study cohort consisted of 46 female and 16 male patients. Clinically significant driver mutations were detected in 58 patients (93.5%). The most commonly observed alteration was TRAF7 mutations (26, 41.9%), followed by AKT1E17K mutations (19, 30.6%). Both mutations were significantly associated with an anterolateral tumor location relative to the brainstem (p = 0.0078). NF2 mutations were present in 11 cases (17.7%) and were associated with posterior tumor location, in contrast to tumors with TRAF7 and AKT1E17K mutations. Other common mutations in FM meningiomas included POLR2A mutations (8, 12.9%; 6 POLR2AQ403K and 2 POLR2AH439_L440del), KLF4K409Q mutations (7, 11.3%), and PIK3CA mutations (4, 6.5%; 2 PIK3CAH1047R and 2 PIK3CAE545K). POLR2A and KLF4 mutations exclusively occurred in female patients and showed no significant association with specific tumor locations. All tumors harboring AKT1E17K and POLR2A mutations displayed meningothelial histology. Ten tumors exhibited intratumoral calcification, which was significantly more frequent in NF2-mutant compared with AKT1-mutant FM meningiomas (p = 0.047). CONCLUSIONS: These findings provide important insights into the molecular genetics and clinicopathological characteristics of FM meningiomas. The identification of specific genetic alterations associated with tumor location, volume, calcification, histology, and sex at diagnosis may have implications for personalized treatment strategies in the future.