Background. Timely diagnosis of the transition from relapsing-remitting multiple sclerosis (MS) to secondary progressive multiple sclerosis (SPMS) is extremely difficult due to the lack of clear criteria characterizing this period of the disease. The choice of therapeutic strategies in this case is a difficult task, and is associated by additional difficulties in the treatment of patients with low treatment adherence.
Description of a clinical case. A clinical case illustrating the difficulty in determining the type of MS is presented for consideration. The questions had to be resolved: remitting or secondary progressive course of the disease and, if SPMS, then with or without exacerbations? A patient who had suffered from MS for 18 years showed an increase in neurological symptoms over 1.5 years by 1 point on the EDSS scale, and an increase in the number of lesions in an MRI study. However, there were certain difficulties in interpreting these changes: they occurred as a result of exacerbation or progression of the disease. A comprehensive assessment of the data, based on current clinical guidelines and modern ideas about the management of MS patients, made it possible to select the optimal treatment strategy for MS patients with low treatment adherence.
Conclusion. A thorough analysis of the available clinical and radiological data of patients with MS, an attentive, trusting relationship between the attending physician and the patient, and the involvement of the patient and his relatives in discussing the choice of therapy are an important component in the practice of a neurologist. Wide therapeutic options and the emergence of innovative drugs contribute to a patient-centered approach to the treatment of MS.

Keywords: siponimod, disease-modifying drugs for multiple sclerosis, secondary progressive multiple sclerosis, treatment adherence