Chronic pain may affect 30–50% of the world’s population and an important cause is small fiber neuropathy (SFN). Recent research suggests that autoimmune diseases may be one of the most common causes of small nerve fiber damage. There is low awareness of SFN among patients and clinicians and it is difficult to diagnose as routine electrophysiological methods only detect large fiber abnormalities, and specialized small fiber tests, like skin biopsy and quantitative sensory testing, are not routinely available. Corneal confocal microscopy (CCM) is a rapid, non-invasive, reproducible method for quantifying small nerve fiber degeneration and regeneration, and could be an important tool for diagnosing SFN. This review considers the advantages and disadvantages of CCM and highlights the evolution of this technique from a research tool to a diagnostic test for small fiber damage, which can be a valuable contribution to the study and management of autoimmune disease.

One of the most important complications of the post-COVID-19 syndrome may be a small fiber neuropathy, which cannot be evaluated by a routine electroneuromyography. Confocal microscopy of the cornea (CCM) may be a promising method for early neuropathy verification. To study the possibility of the small fiber neuropathy evaluation using the CCM in a patient with the post-COVID-19 condition. The patient is a female of 61 years old, which suffered from a COVID-19 infection in October 2020. After a month, she noted the presence of myalgia and polyneuropathy. A year after the onset of the disease, in addition to myalgia, headaches, neuropathy pain, the patient also experienced bowel disorders and stomach aches, which cannot be explained with an alternative diagnosis. The patient underwent CCM to assess the structure of nerve fibers to prove the presence of the small fiber neuropathy as a complication of the COVID-19 infection. The presence of the small fiber neuropathy was evaluated in the patient as well as enlarged Langerhans cells in the cornea. Considering the pivotal role of these cells in the immunological processes, the "activated" dendritic cells in post-COVID-19 patients may serve as another evidence of the autoimmune nature of this complication and possibly, a method for the monitoring treatment effectiveness of this disease. In this clinical case of a 61-year-old patient with the post-COVID-19 syndrome, the possibility of application of the confocal microscopy of the cornea for the diagnosis of neuropathy of small fibers and monitoring of the patient›s condition is shown.

In 2020, the world suffered an epidemic of a new coronavirus infection, after which it became obvious that the consequences of this disease persist for a long time after the recovery, perhaps, for several months. This complication was called post-COVID-19 syndrome and was recognized by the World Health Organization, which was reflected in the Delphi Consensus on October 6, 2021. The clinical characteristics of this disease include a significant number of immunological manifestations, including fever, arthralgia, myalgia, flu-like symptoms, as well as autoimmune diseases manifestation. These symptoms may allude the autoimmune genesis of the COVID-19 complications. This mini-review summarizes the current understanding of the systemic manifestations of COVID-19 and the possible role of impaired immune function in the pathogenesis of post-COVID-19 syndrome.

Introduction: Diabetic neuropathy (DN) affects up to 50% of patients with type 1 diabetes mellitus (T1DM). Clinical manifestations include painful polyneuropathy with autonomic and orthostatic symptoms. Corneal confocal microscopy (CCM) is one of the promising non-invasive methods for DN evaluation and tracking the effectiveness of treatment. Objectives: To perform the early diagnosis of DN in T1DM patients and describe the morphological changes in nerve fibers during the treatment process. Patients and Methods: This prospective study included 77 T1DM patients and 42 healthy controls. All patients underwent CCM and electroneuromyography (ENMG). Twenty-five patients with T1DM and HbA1c 7-10% underwent strict glycemic control with the correction of insulin therapy and the subsequent CCM and ENMG investigations for the second time. Results: In T1DM patients a decrease in the main nerve trunks with age was revealed, as well as an increase in corneal nerve tortuosity (P<0.05). The number of branches of nerve fibers did not change with the increasing age (P=0.07). After reaching T1DM compensation, patients underwent a course of alpha-lipoic acid therapy. Confocal microscopy of the cornea parameters did not undergo significant changes during therapy since significant positive dynamics were noted only in the tortuosity of nerve fibers (P<0.05), which decreased by 11.8%. Conclusion: In patients with T1DM, strict glycemic control, correction of insulin therapy, and courses of alpha-lipoic acid prescription help to reduce the morphological changes of small fiber neuropathy, which can be evaluated by the confocal microscopy of the cornea.