system
Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
user
A patient of rheumatoid arthritis presents with progressive quadri-paresis and weakness, Babinsky sign was positive, increased muscle tone of limbs with exaggerated tendon jerks and worsening of gait with no sensory, sphincter involvement. Best initial investigation is-
assistant
The correct answer is  None