RHEUMATOLOGY
INFECTIOUS ARTHRITIS & BURSITIS
ETIOLOGIES & DIAGNOSIS OF INFECTIOUS ARTHRITIS
Etiologies
• Bacterial (nongonococcal): early diagnosis required
• Gonococcal (N. gonorrhea): consider in sexually active young adults
• Viral: parvovirus, HCV, HBV, acute HIV; typically polyarticular, may mimic RA
• Mycobacterial: monoarticular or axial (Pott’s disease)
• Fungal: Candida (esp. prosthetic joints), coccidiomycosis (valley fever), histoplasmosis
• Other: Lyme, mycoplasma
Diagnosis (JAMA 2007;297:1478)
• H&P w/ poor sensitivity and specificity for septic arthritis; ∴ arthrocentesis should be performed as soon as suspected
• Take care not to tap through an infected area thus introducing infxn into joint space
• ✓ Synovial fluid cell count, Gram stain, bacterial culture, crystals
WBC >50k w/ poly predom suspicious for bact. infxn; crystals do not r/o septic arthritis!
BACTERIAL (NONGONOCOCCAL) ARTHRITIS
Epidemiology & risk factors
• Immunocompromised host: diabetics, HIV, elderly, SLE, etc.
• Damaged joints: RA, OA, gout, trauma, prior surgery/prosthetic, prior arthrocentesis (rare)
• Bacterial seeding: bacteremia secondary to IVDU, endocarditis or skin infection
direct inoculation or spread from contiguous focus (eg, cellulitis, septic bursitis, osteo)
Clinical manifestations (JAMA 2007;297:1478; Lancet 2010;375:846)
• Acute onset monoarticular arthritis (>80%) w/ pain (Se 85%), swelling (Se 78%), warmth
• Location: knee (most common), hip, wrist, shoulder, ankle. In IVDU, tends to involve other areas (eg, sacroiliac joint, symphysis pubis, sternoclavicular and manubrial joints).
• Constit. sx: fevers (Se 57%), rigors (Se 19%), sweats (Se 27%), malaise, myalgias, pain
• Infection can track from initial site to form fistulae, abscesses or osteomyelitis
• Septic bursitis must be differentiated from septic intra-articular effusion
Additional diagnostic studies (JAMA 2007;297:1478)
• Synovial fluid: WBC usually >50k (Se 62%, Sp 92%) but can be <10k, >90% polys; Gram stain 
in ~75% of Staph, ~50% of GNR; Cx in >90%.
Synovial bx for Cx most sens.
• Leukocytosis (Se 90%, Sp 36%)
• Blood cultures in >50% of cases, ~80% when more than 1 joint involved
• Conventional radiographs usually normal until after ~2 wk of infection when bony erosions, joint space narrowing, osteomyelitis, periostitis can be seen
• CT & MRI useful esp. for suspected hip infection or epidural abscess
Treatment (for native joints)
• Prompt empiric antibiotics guided by Gram stain after surgical drainage. If Gram stain 
, empiric Rx w/ vancomycin; add anti-pseudomonal agent if elderly, immunosupp.
• Tailor antibiotics based on Gram stain, culture results, & clinical course
• IV antibiotics × ≥2 wk followed by oral antibiotics; varies by clinical course & microbiology
• Joint must be drained, often serially; surgical drainage (usually arthroscopic), esp. for larger joints and as initial treatment, but may also be accomplished by arthrocentesis.
Serial synovial fluid analyses should demonstrate ↓ in WBC and sterility.
• Prognosis: 10–50% mortality depending on virulence of organism, time to Rx, host
Prosthetic joint infections (Infect Dis Clin North Am 2012;26:29; CID 2013;66:e1)
• ↑ risk in first 2 y s/p procedure; rate generally low (0.5–2.4%); risk factors include obesity, RA, immunocompromised state, steroids, & superficial surgical site infxn
• Staphylococci (coag negative & S. aureus) in >50%; polymicrobial in 10–20%
• Early (<3 mo s/p surgery) or delayed (3–24 mo) onset typically acquired during implantation; early w/ virulent organisms (eg, MRSA) and delayed w/ less virulent organisms (eg, P. acnes, coag negative Staph) & more indolent presentation
• Late (>24 mo) onset typically related to secondary hematogenous seeding
• Diagnosis requires arthrocentesis by orthopedics; ESR & CRP can be helpful
• Treatment typically requires prolonged abx & two-stage joint replacement (joint retention a/w ~40% failure rate; CID 2013;56:182) or life-long suppressive abx. ID and orthopedics consultation required.
DISSEMINATED GONOCOCCAL INFECTION (DGI)
Epidemiology (Infect Dis Clin North Am 2005;19:853)
• N. gonorrhea; most frequent type of infectious arthritis in sexually active young adults
• Normal host as well as Pts w/ deficiencies of terminal components of complement
• 
:
=4:1; ↑ incidence during menses, pregnancy, & postpartum period; ↑ incidence in homosexual males; rare after age 40 y
Clinical manifestations
• Preceded by mucosal infection (eg, endocervix, urethra or pharynx) that is often asx
• Two distinct syndromes:
Joint localized: purulent arthritis (40%), usually 1–2 joints (knees > wrists > ankles)
DGI: triad of polyarthralgias, tenosynovitis, skin lesions; purulent arthritis rare
acute onset of tenosynovitis (60%) in wrists, fingers, ankles, toes rash (>50%): gunmetal gray pustules with erythematous base on extremities & trunk
• Rare complications: Fitz-Hugh-Curtis syndrome (perihepatitis), pericarditis, meningitis, myocarditis, osteomyelitis from direct extension of joint-localized infection
Additional diagnostic studies
• Synovial fluid: WBC >50k (but can be <10k), poly predominant
Gram stain in ~25%; culture in up to 50% if done w/ Thayer-Martin media
• Blood culture: more likely in DGI; rarely in joint localized disease
• Gram stain and culture of skin lesions occasionally
• Cervical, urethral, pharyngeal, rectal PCR or cx on Thayer-Martin media; ✓ Chlamydia
Treatment
• Ceftriaxone or cefotaxime ¥ 7 Δ w/ empiric doxycycline for Chlamydia (fluoroquinolones no longer recommended due to resistance)
• Joint arthroscopy/lavage may be required if purulent arthritis; rarely >1 time
OLECRANON & PREPATELLAR BURSITIS
Epidemiology & risk factors (Infect Dis North Am 2005;19:991)
• >150 bursae in the body; 2 most commonly infected are olecranon and prepatellar
• Most commonly (esp. superficial bursae) due to direct trauma, percutaneous inoculation or contiguous spread from adjacent infection (eg, cellulitis)
• Other risk factors: recurrent noninfectious inflammation (eg, gout, RA, CPPD), diabetes
• S. aureus (80%) most common, followed by streptococci
Diagnosis
• Physical exam: discrete bursal swelling, erythema, maximal tenderness at center of bursa with preserved joint range of motion
• Aspirate bursa if concern for infxn, ✓ cell count, Gram stain, bacterial cx, crystals
WBC >20k w/ poly predominance suspicious for bacterial infection, but lower counts common (crystals do not rule out septic bursitis!)
• Assess for adjacent joint effusion, which can also be septic
• Take care not to tap through infected skin thus introducing infxn into bursa
Initial therapy
• Prompt empiric coverage for staphylococci and streptococci: PO abx acceptable for mild presentation; vancomycin if ill-appearing; broaden spectrum based on risk factors
• Modify antibiotics based on Gram stain, culture results, & clinical course
• Duration of therapy is 1–4 wk
• Serial aspirations every 1–3 Δ until sterile or no reaccumulation of fluid
• Surgery if unable to drain bursa through aspiration, evidence of foreign body or necrosis, recurrent/refractory bursitis w/ concern for infxn of adjacent structures