Studying serum neurofilament light chain levels as a potential new biomarker for small fiber neuropathy.

BACKGROUND AND PURPOSE: Diagnosing small fiber neuropathies can be challenging. To address this issue, whether serum neurofilament light chain (sNfL) could serve as a potential biomarker of damage to epidermal Aδ- and C-fibers was tested. METHODS: Serum NfL levels were assessed in 30 patients diagnosed with small fiber neuropathy and were compared to a control group of 19 healthy individuals. Electrophysiological studies, quantitative sensory testing and quantification of intraepidermal nerve fiber density after skin biopsy were performed in both the proximal and distal leg. RESULTS: Serum NfL levels were not increased in patients with small fiber neuropathy compared to healthy controls (9.1 ± 3.9 and 9.4 ± 3.8, p = 0.83) and did not correlate with intraepidermal nerve fiber density at the lateral calf or lateral thigh or with other parameters of small fiber impairment. CONCLUSION: Serum NfL levels cannot serve as a biomarker for small fiber damage.

Phenotyping peripheral neuropathies with and without pruritus: a cross-sectional multicenter study.

ABSTRACT: Pruritus often escapes physicians' attention in patients with peripheral neuropathy (PNP). Here we aimed to characterize neuropathic pruritus in a cohort of 191 patients with PNP (large, mixed, or small fiber) and 57 control subjects with deep phenotyping in a multicenter cross-sectional observational study at 3 German sites. All participants underwent thorough neurological examination, nerve conduction studies, quantitative sensory testing, and skin biopsies to assess intraepidermal nerve fiber density. Patients filled in a set of questionnaires assessing the characteristics of pruritus and pain, the presence of depression and anxiety, and quality of life. Based on the severity of pruritus and pain, patients were grouped into 4 groups: "pruritus," "pain," "pruritus and pain," and "no pruritus/no pain." Although 11% (21/191) of patients reported pruritus as their only symptom, further 34.6% (66/191) reported pruritus and pain. Patients with pain (with or without pruritus) were more affected by anxiety, depression, and reduced quality of life than control subjects. Patients with pruritus (with and without pain) had increases in cold detection threshold, showing Aδ-fiber dysfunction. The pruritus group had lower intraepidermal nerve fiber density at the thigh, concomitant with a more proximal distribution of symptoms compared with the other PNP groups. Stratification of patients with PNP by using cross-sectional datasets and multinominal logistic regression analysis revealed distinct patterns for the patient groups. Together, our study sheds light on the presence of neuropathic pruritus in patients with PNP and its relationship with neuropathic pain, outlines the sensory and structural abnormalities associated with neuropathic pruritus, and highlights its impact on anxiety levels.

Brain connectivity networks underlying resting heart rate variability in acute ischemic stroke.

Acute strokes can affect heart rate variability (HRV), the mechanisms how are not well understood. We included 42 acute stroke patients (2-7 days after ischemic stroke, mean age 66 years, 16 women). For analysis of HRV, 20 matched controls (mean age 60.7, 10 women) were recruited. HRV was assessed at rest, in a supine position and individual breathing rhythmus for 5 min. The coefficient of variation (VC), the root mean square of successive differences (RMSSD), the powers of low (LF, 0.04-0.14 Hz) and high (HF, 0.15-0.50 Hz) frequency bands were extracted. HRV parameters were z-transformed related to age- and sex-matched normal subjects. Z-values < -1 indicate reduced HRV. Acute stroke lesions were marked on diffusion-weighted images employing MRIcroN and co-registered to a T1-weighted structural volume-dataset. Using independent component analysis (ICA), stroke lesions were related to HRV. Subsequently, we used the ICA-derived lesion pattern as a seed and estimated the connectivity between these brain regions and seven common functional networks, which were obtained from 50 age-matched healthy subjects (mean age 68.9, 27 women). Especially, LF and VC were frequently reduced in patients. ICA revealed one covarying lesion pattern for LF and one similar for VC, predominantly affecting the right hemisphere. Activity in brain areas corresponding to these lesions mainly impact on limbic (r = 0.55 ± 0.08) and salience ventral attention networks (0.61 ± 0.10) in the group with reduced LF power (z-score < -1), but on control and default mode networks in the group with physiological LF power (z-score > -1). No different connectivity could be found for the respective VC groups. Our results suggest that HRV alteration after acute stroke might be due to affecting resting-state brain networks.

Nociceptive two-point discrimination acuity and body representation failure in polyneuropathy.

OBJECTIVES: Although patients' complaints suggest polyneuropathy (PNP) and neuropathic pain, routine investigations do not always support the diagnosis. Assessing two-point-pain discrimination thresholds (2ptDT) and quantify body representation disturbances might be useful to close this diagnostic gap. METHODS: Pinprick pain and laser-heat pain perception thresholds and 2ptDT on hands, forearms, lower legs and feet were obtained in 20 PNP patients (mean age: 57.6 ± 13.9) and 20 healthy subjects (mean age: 50.6 ± 4.7 years). Body representation disturbances were assessed by self-estimating feet size and the Bath CRPS body perception disturbances questionnaire adapted for PNP. RESULTS: Pain perception thresholds and laser-heat pain 2ptDT were unaltered, but patients had higher pinprick pain 2ptDT then the healthy subjects. The 2ptDT for pinprick at the hands discriminate best between groups (U-test; p=0.001). Furthermore, patients estimated their feet longer than they are. In subsequent multivariate discriminant analyses, 2ptDT for pinprick pain at the hands, 2ptDT for laser-heat pain and the perception thresholds for laser-heat pain at the feet classified 85% of PNP vs. HC correctly. The combination of 2ptDT for pinprick pain at the hands, pinprick pain perception thresholds at the calves and foot length estimation differentiates painful vs. non-painful PNPs correctly in 90% of the cases. CONCLUSIONS: Testing 2ptDT for painful pinprick stimuli at the hands and asking for foot length estimation might add to diagnostic accuracy in painful PNP.