Differentials: Monoarticular Arthritis

Ascertain inflammation (arthritis) is present by eliciting pain on joint motion.

Differentials:
1. Trauma
2. Gout - Recurrent attacks, rapid response, e.g. to colchicine, and tophi are clues, as well as favored sites such as 1st MTPJ (less common sites: ankles, knees, wrist, olecranon bursa)
3. OA - Monoarticular arthritis usually occurs as a flare-up of longstanding OA. Look for crepitus within the range of motion.
4. Pseudogout
5. Septic arthritis - fevers, chills, joint pain that is progressive, throbbing, and severe. Hot/tender joint to touch.
6. Septic bursitis - Think of this when cellulitis is present, e.g. prepatellar or olecranon bursa, with normal join motion. Accompanied by fever, w/w/o lymphangitis.
7. Lyme disease - Recent travel, flu-like illness, fever, arthralgias, expanding annular red rash with clear center (target lesion; erythema migrans) preceding arthritis by days-months.
8. Gonococcal arthritis - Sexually active adult. Initial phase of fever, polyarthralgia, tenosynovitis, and pustular or necrotic skin lesions is followed by a septic joint. Urethritis or cervicitis (w/w/o purulent discharge) may be present.
9. Avascular necrosis - Consider this in patients on steroids, or where air/fat/nitrogen embolism may be present.
10. Presentation of a polyarticular disease - RA, AnkSpon, Reiter/s (+- urethritis), psoriatic, IBD, and sarcoidosis. If migrating polyarticular, think of rheumatic fever (Group A streptococcus).
11. Bleeding disorder - Consider if hemarthrosis is suspected.