Myofascial pain syndrome, also known as chronic myofascial pain, is a musculosketal pain condition characterized by trigger points (trigger points in MPS should not be confused with tender points in fibromyalgia) which are painful abnormal points in the muscles tissues. Trigger points feels like a small knot under your skin and can be painful when pressure is applied or cause pain in unrelated areas (this is known as referred pain).
Trigger points usually form after some kind of muscle trauma where muscle tissues are damaged. Studies suggest that the injured muscle tissues of MPS patients heals abnormally where nerve cells connect to muscle cells forming trigger points. This points to MPS being a neuromuscular disease.
Similar to fibromyalgia, MPS is a condition causing pain in the musculoskeletal system. However, in the case of MPS, the pain is localized unlike fibromyalgia where pain is believe to be centralized. It remains unclear why people with MPS tend to develop fibromyalgia later on but various studies have suggested that chronic pain conditions, not limited to MPS, can alter the behaviour of the brain and central nervous system causing increased central sensitivity. Hence it is believed that early treatment of MPS, or other chronic pain, can reduce risk of developing fibromyalgia.