State of corneal nerve fibers in systemic amyloidosis

The term systemic amyloidosis unites a group of diseases with a single pathogenetic mechanism involving diffuse deposition of a pathological fibrillar protein (amyloid) in the intercellular space of various organs. Among the systemic forms of amyloidosis, light chain amyloidosis (AL-amyloidosis) occurs most often in clinical practice, while transthyretin amyloidosis (TTR-amyloidosis) is its most common hereditary form. Laser corneal confocal microscopy (CCM) allows for in vivo and non-invasive assessment of the state of corneal nerve fibers (CNF). Purpose To assess the state of CNF in systemic amyloidosis by confocal microscopy data obtained in vivo. Material and methods The main study group included 16 patients (6 men and 10 women, mean age 60.5±11.6 years) with morphologically confirmed primary AL-amyloidosis, and 14 patients (5 men and 9 women, mean age 59.4±11.3 years) with genetically and morphologically confirmed hereditary TTR-amyloidosis. The control group included 23 healthy volunteers of the same age range without any neurological pathologies. The state of CNF was assessed by in vivo CCM data recorded on the HRT III system and its consequently processing using authors' self-developed program Liner 1.2. The criteria for neuropathy intensity was the degree of CNF tortuosity characterized by coefficients of anisotropy (KΔL) and symmetry (Ksym) of CNF orientation. Results According to the NIS scale, the manifestations of neuropathy in the subgroup of patients with TTR-amyloidosis were significantly more pronounced compared to AL-amyloidosis patients. The severity of clinical manifestations of neuropathy did not depend on the duration of TTR-amyloidosis and AL-amyloidosis (Spearman R rs=0.21, p=0.58 and rs= -0.49, p=0.055, respectively). Changes in the quantitative indicators (a decrease in the anisotropy coefficient and an increase in the symmetry coefficient of the fibers orientation) confirm increased tortuosity of CNF in systemic amyloidosis. Conclusion The clinical picture of systemic amyloidosis is characterized by polymorphism of neurological manifestations that include various symptoms of damage to the peripheral somatic and autonomic nervous system. In vivo CCM can be used to reveal qualitative and quantitative changes in CNF in patients with systemic amyloidosis. However, statistical unreliability of the identified quantitative changes allows considering the state of CNF in amyloidosis only as a component of the disease monitoring algorithm, but not as a biomarker of the disease.