What causes middle back pain?

Muscular v disc: This could be muscular pain or related to underlying degenerative discs or even a herniated disc or other spine based conditions. Other issues could include referred pain from a lung or pulmonary issue or gastrointestinal issue like an esophagitis, ulcer, gallstones or reflux. Even a renal or kidney issue may be a cause. See your doctor if symptoms persist or worsen.