If a patient has the typical symptoms and radiographic features described above, the diagnosis of OA is relative straightforward and is unlikely to be confused with other entities. However, in less straightforward cases, other diagnoses should be considered:
- Periarticular structure derrangement: Periarticular pain that is not reproduced by passive motion or palpation of the joint should suggest an alternate etiology such as bursitis, tendonitis or periostitis.
- Inflammatory arthritis: If the distribution of painful joints includes MCP, wrist, elbow, ankle or shoulder, OA is unlikely, unless there are specific risk factors (such as occupational, sports-related, history of injury). Prolonged stiffness (greater than one hour) should raise suspicion for an inflammatory arthritis such as rheumatoid arthritis. Marked warmth and erythema in a joint suggests a crystalline etiology. Arthrocentesis (aspiration of the joint) can help aid in distinuishing between these types of arthritis if the diagnosis is not clear by history, physical exam, and radiographs. If there is any suggestion of an infected joint, it should be aspirated and the fluid sent for culture as well.
- Other inflammatory / systemic condition: Weight loss, fatigue, fever and loss of appetite suggest a systemic illness such as polymyalgia rheumatica, rheumatoid arthritis, lupus or sepsis or malignancy.
