135 Ch 135. Infectious Arthritis

感染性關節炎 (Septic arthritis) 是骨關節急症 — 24-48 小時內未引流 cartilage 即可永久損傷，因為 pus 內的 proteolytic enzyme 會快速破壞 articular cartilage。核心鐵則：「急性 monoarthritis = septic arthritis until proven otherwise」，即使 gout/CPPD 結晶看到也不能放心 (crystals + septic 可同時存在)，必須抽關節液 + Gram stain + culture 才能確診。Synovial fluid analysis 是診斷主力：Normal (< 200 WBC, < 25% PMN, clear)；Inflammatory (gout/RA, 2,000-50,000 WBC, > 50% PMN, yellow)；Septic (> 50,000 WBC 多 100K+, > 75-90% PMN, cloudy/purulent, glucose 大降, Gram + ~ 40-50%, culture + ~ 90%)；Crystal (MSU 痛風 / CPPD 假痛風, 可重疊 septic 數值)。病原依族群：成人 (sexually active) → N. gonorrhoeae (DGI) + S. aureus + Strep 共同 cover；老人 / 免疫低下 / IVDU / HCAI → S. aureus (含 MRSA) + Gram-negative；兒童 < 4 歲 → Kingella kingae (#1) + S. aureus + S. pyogenes (NB: Kingella 培養難長, 需 PCR)；Prosthetic joint → CoNS (S. epidermidis) + S. aureus + S. viridans (依 timing)；動物咬傷 → Pasteurella multocida (貓) / Eikenella corrodens (人)；tick-bite (北美 endemic) → Borrelia burgdorferi (Lyme arthritis)。Empirical 抗生素：Native joint healthy adult → Vancomycin + Ceftriaxone (cover MRSA + DGI + most pathogens)；IVDU / HCAI → Vancomycin + Pip-tazo 或 Cefepime (cover Pseudomonas)；Prosthetic joint → Vancomycin + Cefepime ± Rifampin (rifampin penetrates biofilm, 對 staph 必加)；culture 出來後 narrow spectrum。Treatment duration：Native S. aureus 2-4 週 IV、native Gram-/GAS 2 週、DGI 7-14 天、Prosthetic 6-8 週 + DAIR / 2-stage revision、Mycobacteria/fungi 數月至年。Disseminated Gonococcal Infection (DGI) — 國考高頻：1-3% 淋病進展為 DGI；經典三聯 = (1) Tenosynovitis (asymmetric, 手腳手腕腳踝)、(2) Migratory polyarthralgia (transient)、(3) Dermatitis (pustular/papular skin lesions)；joint aspiration culture 常陰性 (~50%)，urethra/cervix/throat/rectum PCR 高 yield；治療 = Ceftriaxone 1g IV daily × 7-14 d + Doxycycline 或 Azithromycin (cover concomitant Chlamydia)。Drainage strategies：Daily aspiration (大關節 traditional)、Arthroscopic / open lavage (hip、複雜、prosthetic、refractory)、Hip septic arthritis 6 小時內緊急 OR drainage (因為 hip joint compartment 高壓 → cartilage 損害速度最快)。特殊原因：Lyme arthritis — 北美/歐洲 (台灣罕見)，多 late manifestation (EM rash 後數月)，膝為最常見大關節，serology two-tier (ELISA → Western blot)，Doxycycline 100 mg BID × 28 d；TB arthritis — hematogenous from 1° TB (常 years later)，Pott’s disease (脊椎) > peripheral joints，synovial biopsy + AFB culture + GeneXpert MTB，治療 = 4-drug RIPE × 2 mo + 7 mo INH/RIF = 9 個月 total；Fungal arthritis — Candida (prosthetic, CRBSI, IVDU)、Sporothrix (gardener, 玫瑰刺)、Coccidioides/Histoplasma/Blastomyces (endemic mycosis)，治療 = amphotericin B → azole 長療程；Reactive arthritis (Reiter’s) — post-infectious 非直接感染, 1-4 週後 GI (Yersinia/Campylobacter/Salmonella) 或 GU (Chlamydia) 感染，三聯 = arthritis + uveitis/conjunctivitis + urethritis, HLA-B27 association, 治療 NSAIDs + 治原發 + DMARDs if persistent。Prosthetic Joint Infection (PJI) — Specialist 重點：分型 — Early (< 3 mo post-op, 手術污染) / Delayed (3-12 mo, less virulent) / Late (> 12 mo, hematogenous from dental/skin/UTI)；Treatment options — DAIR (Debride, Antibiotic, Implant Retention): 表淺 acute, < 4 週症狀, antibiotic 6-12 wk; One-stage revision: known organism + good soft tissue; Two-stage revision (gold standard): explant → spacer + 6 wk IV → reimplant; Permanent fusion / amputation: refractory 個案; Rifampin add-on for Staphylococcus (penetrates biofilm) 是 PJI 治療的關鍵。22e 重點：N. gonorrhoeae XDR strains 出現 (ceftriaxone 仍 first-line 但 surveillance 重要)、Lyme arthritis post-treatment (PTLDS) 不建議延長 antibiotic (sx 持續多為 immune-mediated 非持續感染)、DAIR 在 early acute PJI 越來越被接受。台灣 context：細菌性關節炎主流 S. aureus、DGI 隨 STD 上升而增加、健保 vancomycin / linezolid / daptomycin 需 ID consult、TB arthritis 仍 endemic 區可見 但少。