Possible causes of right upper back pain in the evening but not during the day include dorsal fasciitis, muscle strain in the right shoulder blade, ankylosing spondylitis, and spinal tumor. 1. Dorsal fasciitis: Pain in the upper right back occurs when there is dorsal fasciitis caused by long-term exertion or cold. The pain is more obvious at night because the local blood circulation slows down and inflammatory irritants accumulate during sleep. During the daytime, the local blood circulation is faster and the pain is relatively insignificant. 2. Muscle strain in the right scapula: The muscles located in the back, such as the latissimus dorsi, rhomboid, rhomboid, and trapezius, are also distributed around the scapula, which are overworked during the day and produce muscle strain. Excessive accumulation of lactic acid in the muscles of the right scapula during evening rest stimulates the nerve endings and causes pain in the right upper shoulder. 3. Ankylosing spondylitis: Ankylosing spondylitis caused by genetic, environmental, immune, infectious and other factors may also present the symptoms of right upper back pain, and the pain is more obvious in the evening because the pain is improved by moving the thoracic vertebrae, lumbar vertebrae and joints in the daytime, which results in the phenomenon of right upper back pain in the evening and pain in the daytime. 4. Spinal tumor: If the vertebrae or accessories of spine, primary tumor or metastatic tumor occurs, the symptom of right upper back pain may appear. The pain may be caused by the direct stimulation of the tumor site due to the compression effect and involuntary activity of the body during the night sleep. There may be other reasons for right upper back pain in the evening but not in the daytime. It is recommended to go to regular hospitals in time to improve the relevant examinations, clarify the cause of the disease, and then give targeted treatment or therapy under the guidance of the doctor.