A 52-year-old patient works as a secretary and has 30 year record of service. She complains of spasms in her right hand during working and inability to type and write. Up to 80% of her work involves hand load. The patient has been presenting with these symptoms for 2 years. Objectively: the right hand is tense, there is an increase in muscle tone, attempts to write cause spasms. Examination revealed no pathological changes of CNS. What is the most likely diagnosis?