Changes in the synovial membrane may lead to a reduction in lubrication of the joint and contribute to degenerative joint changes. The muscles become weak, and fibrosis may occur. All these factors may lead to a further limitation of jaw movement and increase in pain. Degenerative joint disease, such as osteoarthritis or organic degeneration of the articular surfaces, recurrent fibrous or bony ankylosis, developmental abnormality, or pathologic lesions within the TMJ. Myofascial pain syndrome. Referred TMD pain Sometimes TMD pain can radiate or be referred from its cause (i.e. the TMJ or the muscles of mastication) and be felt as headaches, earache or toothache. Due to the proximity of the ear to the temporomandibular joint, TMJ pain can often be confused with ear pain. The pain may be referred in around half of all patients and experienced as otalgia (earache). Conversely, TMD is an important possible cause of secondary otalgia. Treatment of TMD may then significantly reduce symptoms of otalgia and tinnitus, as well as atypical facial pain. Despite some of these findings, some researchers question whether TMJD therapy can reduce symptoms in the ear, and there is currently an ongoing debate to settle the controversy. Diagnosis Pain is the most common reason for people with TMD to seek medical advice. Joint noises may require auscultation with a stethoscope to detect. Clicks of the joint may also be palpated, over the joint itself in the preauricular region, or via a finger inserted in the external acoustic meatus, which lies directly behind the TMJ. The differential diagnosis is with degenerative joint disease (e.g. osteoarthritis), rheumatoid arthritis, temporal arteritis, otitis media, parotitis, mandibular osteomyelitis, Eagle syndrome, trigeminal neuralgia, oromandibular dystonia, deafferentation pains, and psychogenic pain. Diagnostic criteria Various diagnostic systems have been described. Some consider the Research Diagnostic Criteria method the gold standard. Abbreviated to "RDC/TMD", this was first introduced in 1992 by Dworkin and LeResche in an attempt to classify temporomandibular disorders by etiology and apply universal standards for research into TMD. This method involves 2 diagnostic axes, namely axis I, the physical diagnosis, and axis II, the psychologic diagnosis. Axis I contains 3 different groups which can occur in combinations of 2 or all 3 groups, (see table). McNeill 1997 described TMD diagnostic criteria as follows: Pain in muscles of mastication, the TMJ, or the periauricular area (around the ear), which is usually made worse by manipulation or function. Asymmetric