Rheumatology and Orthopedics
The acutely hot joint
Aspirate before giving antibiotics. Gout shows negatively birefringent needle-shaped crystals; pseudogout shows positively birefringent rhomboid crystals with chondrocalcinosis. Crystal disease does not exclude infection - send cell count, Gram stain, and culture. Septic arthritis requires urgent drainage and intravenous antibiotics; in sexually active young adults consider Neisseria gonorrhoeae. Do not stop allopurinol during a flare, and start urate-lowering therapy only with anti-inflammatory prophylaxis.
Inflammatory arthritis
Rheumatoid arthritis is symmetric, involves small joints and the MCP/PIP joints, spares the DIP joints, and is seropositive for anti-CCP in most cases. Screen for latent tuberculosis and hepatitis B before starting biologics, and monitor methotrexate with CBC and liver enzymes. Systemic lupus erythematosus is suggested by ANA plus anti-dsDNA or anti-Smith, low complement, and multi-organ involvement; assess urine protein for nephritis and avoid sulfonamides.
Vasculitis and polymyalgia
Giant cell arteritis and polymyalgia rheumatica cause a markedly elevated ESR with proximal aching; visual symptoms or jaw claudication mandate immediate high-dose steroids before temporal artery biopsy. ANCA-associated vasculitis causes pulmonary-renal syndrome with sinus and renal involvement.
Orthopedics
Recognize red flags in back pain: fever, cancer history, night pain, neurologic deficits, bowel or bladder changes, and age over 50 with new pain. Osteoporosis is defined by a T-score of −2.5 or lower; treat with bisphosphonates and adequate calcium and vitamin D.
Worked example
A monoarthritis with Gram-positive cocci on Gram stain is septic until proven otherwise: aspirate, start empiric antibiotics, and obtain surgical drainage.