Massachusetts regulators revoked or suspended the professional licenses of 13 nurses after discovering recently that the health care workers lied about having nursing degrees or being licensed in other states, health department documents show. The action sparked questions about the background checks state regulators rely on to issue licenses to thousands of nurses and applicants in 10 other health fields, including pharmacists, psychologists, podiatrists, and optometrists. And the discovery raised the unsettling prospect that patients might have been treated by health care workers with fraudulent credentials, although regulators said there is no evidence so far linking the nurses to any patient safety or quality of care issues.