Small fibre neuropathy assessments in early stages of hATTR amyloidosis

Cutaneous biomarkers of therapeutic efficacy in early treatment of hereditary ATTR amyloid polyneuropathy with tafamidis

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.

Corneal confocal microscopy identifies corneal nerve loss and increased Langerhans cells in presymptomatic carriers and patients with hereditary transthyretin amyloidosis

BACKGROUND

Hereditary transthyretin amyloidosis (ATTRv amyloidosis) is a rare, but life-threatening protein misfolding disorder due to TTR gene mutations. Cardiomyopathy (ATTRv-CM) and polyneuropathy (ATTRv-PN) with early small nerve fibre involvement are the most common manifestations. Timely diagnosis and treatment initiation are key to limiting progression of disease. Corneal confocal microscopy (CCM) is a non-invasive method to quantify corneal small nerve fibres and immune cell infiltrates in vivo.

METHODS

This cross-sectional study investigated the utility of CCM in 20 patients with ATTRv amyloidosis (ATTRv-CM, n = 6; ATTRv-PN, n = 14) and presymptomatic carriers (n = 5) compared to 20 age- and sex-matched healthy controls. Corneal nerve fibre density, corneal nerve fibre length, corneal nerve branch density, and cell infiltrates were assessed.

RESULTS

Corneal nerve fibre density and nerve fibre length were significantly lower in patients with ATTRv amyloidosis compared to healthy controls regardless of the clinical phenotype (ATTRv-CM, ATTRv-PN) and corneal nerve fibre density was significantly lower in presymptomatic carriers. Immune cell infiltrates were only evident in patients with ATTRv amyloidosis, which correlated with reduced corneal nerve fibre density.

CONCLUSIONS

CCM identifies small nerve fibre damage in presymptomatic carriers and symptomatic patients with ATTRv amyloidosis and may serve as a predictive surrogate marker to identify individuals at risk of developing symptomatic amyloidosis. Furthermore, increased corneal cell infiltration suggests an immune-mediated mechanism in the pathogenesis of amyloid neuropathy.

Functional and morphometric assessment of small-fibre damage in late-onset hereditary transthyretin amyloidosis with polyneuropathy: the controversial relation between small-fibre-related symptoms and diagnostic test findings

INTRODUCTION

We aimed at investigating whether functional and morphometric tests assessing small-fibre damage, ie quantitative sensory testing, Sudoscan and skin biopsy, reliably reflect neuropathic pain and autonomic symptoms in patients with late-onset hereditary transthyretin amyloidosis with polyneuropathy (ATTRv-PN).

METHODS

In 30 patients with late-onset ATTRv-PN, we collected quantitative sensory testing, Sudoscan and skin biopsy with assessment of intraepidermal, piloerector muscle and sweat gland nerve fibre density. We then correlated these functional and morphometric parameters with neuropathic pain and autonomic symptoms as assessed with the Neuropathic Pain Symptom Inventory (NPSI) and Composite Autonomic Symptom Score-31 (COMPASS-31).

RESULTS

50% of patients showed small-fibre damage in the form of a pure small-fibre neuropathy, 47% in the context of a mixed fibre neuropathy with small and large fibre involvement. All patients complained of at least one autonomic symptom and 60% had neuropathic pain. Whereas quantitative sensory testing and Sudoscan parameters correlated with neuropathic pain and autonomic symptoms as assessed by NPSI and COMPASS-31, intraepidermal, piloerector muscle and sweat gland nerve fibre density quantification did not.

CONCLUSIONS

Our findings indicate that functional test parameters reliably reflect neuropathic pain and autonomic symptoms related to small-fibre damage. These findings might help to identify clinically useful biomarkers to assess patient follow-up.