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BACKGROUND: ATTR (ATTRv) amyloidosis neuropathy is characterized by progressive sensorimotor and autonomic nerve degeneration secondary to amyloid deposition caused by a misfolded transthyretin protein (TTR). Small nerve fiber neuropathy is an early clinical manifestation of this disease resulting from the dysfunction of the Aδ and C small nerve fibers. Tafamidis, a selective TTR stabilizer, has proven its efficacy in the earlier stages of hATTR. OBJECTIVES: To evaluate the clinical course and utility of cutaneous pathological biomarkers in patients with ATTR amyloidosis treated with tafamidis compared to control patients. METHODS: Forty patients diagnosed with early stages of ATTRv amyloidosis (polyneuropathy disability [PND] scores 0-II) underwent small and large nerve fiber neurological evaluations, and annual skin biopsies for intraepidermal nerve fiber density (IENFD) and amyloid deposition index (ADI) estimation. Thirty patients were allocated to receive tafamidis, and 10 patients served as controls. Tafamidis pharmacokinetics analysis was performed in patients who received the treatment. RESULTS: At baseline, 12% of patients in stage PND 0 and 28% in PND I displayed small nerve fiber denervation in the distal thigh, whereas 23% and 38%, respectively, in the distal leg. Similarly, 72% and 84% had amyloid deposition in the distal thigh and 56% and 69% in the distal leg. Following 1 year of treatment, the tafamidis group showed significant clinical improvement compared to the control group, revealed by the following mean differences (1) -9.3 versus -4 points (p = <.00) in the patient's neuropathy total symptom score 6 (NTSS-6) questionnaire, (2) -2.5 versus +2.8 points (p = <.00) in the Utah Early Neuropathy Score (UENS), and (3) +1.2°C versus -0.6 (p = .01) in cold detection thresholds. Among the patients who received tafamidis, 65% had stable or increased IENFD in their distal thigh and 27% in the distal leg. In contrast, all patients in the control group underwent denervation. The ADI either decreased or remained constant in 31% of the biopsies in the distal thigh and in 24% of the biopsies in the distal leg of the tafamidis-treated patients, whereas it rose across all the biopsies in the control group. At the 4-year follow-up, the tafamidis group continued to display less denervation in the distal thigh (mean difference [MD] of -3.0 vs. -9.3 fibers/mm) and the distal leg (mean difference [MD] -4.9 vs. -8.6 fibers/mm). ADI in tafamidis-treated patients was also lower in the distal thigh (10 vs. 30 amyloid/mm2) and the distal leg (23 vs. 40 amyloid/mm2) compared to control patients. Plasma tafamidis concentrations were higher in patients with IENFD improvement and in patients with reduced amyloid deposition. Patients without amyloid deposition in the distal leg at baseline displayed delayed disease progression at 4 years. CONCLUSIONS: Cutaneous IENFD and amyloid deposition assessments in the skin of the distal thigh and distal leg are valuable biomarkers for early diagnosis of ATTR amyloidosis and for measuring the progression of small nerve fiber neuropathy. Early treatment with tafamidis slows the clinical progression of the disease, skin denervation, and amyloid deposition in the skin. Higher plasma concentrations of tafamidis are associated with better disease outcomes, suggesting that increasing the drug dose could achieve better plasma concentrations and response rates. This study describes the longest small nerve fiber neuropathy therapeutic trial with tafamidis and is the first to report small fiber symptoms, function, and structural assessments as outcomes.

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OBJECTIVE: We report the results of a pilot, enrichment-design, placebo-controlled crossover trial of pregabalin for the treatment of prediabetic small-fiber neuropathic pain. METHODS: Individuals with impaired fasting glucose or impaired glucose tolerance and neuropathic pain were evaluated according to UTAH Early Neuropathy Scale (UENS), Quantitative Sensory Testing, and intraepidermal nerve fiber density (IENFD). Symptoms were graded according to the Numeric Rating Scale (NRS). Individuals who responded to the administration of placebo were not eligible. Pregabalin was initiated at a dose of 75 mg qid and tapered up to 300 mg bid. Only individuals with a reduction of pain scores ≥30% were eligible to continue with the double-blind phase, which consisted of a randomized crossover period of 1 month of pregabalin and 1 month of placebo, with 7 days of washout between periods. RESULTS: Forty-five participants were enrolled in the study. There was 36% reduction in the NRS from baseline after 1 month of single-blind pregabalin (NRS=5.1±2.6). Twenty-six participants were eligible for the double-blind phase. There was further reduction of pain in the double-blind pregabalin and the placebo groups, but the pregabalin group had a statistically significant reduction of pain (NRS=3.2±2.2 vs. 4.0±2; P<0.05). Participants who did not respond showed a lower IENFD than those who responded, suggesting more severe nerve damage. CONCLUSIONS: This pilot study showed improvement of prediabetic neuropathic pain. Participants with higher pain scores at baseline had higher UENS scores and a lower IENFD. Limitations of the study include the small number of participants and the carry-over effect.

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