Acute Monoarthritis: A CaseBased Approach

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Acute Monoarthritis A Case-Based Approach

• Paul R. Chelminski, MD, MPH, FACP
• Assistant Professor of Medicine
• Associate Residency Program Director for
  Outpatient Education
• UNC Department of Medicine

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Objectives

• The Resident Will
• Understand common presentations of acute
  monoarthritis
• Learn the differential diagnosis of acute
  monoarthritis
• Understand the microbiologic epidemiologic
  characteristics of infectious monoarthritis
• Understand synovial fluid analysis

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Case 1 Hx

• 35yo female with one day h/o painful swollen
  wrist
• Fever to 103F chills
• Med OCPs
• Sexually active with husband
• ROS Neg. for Vag. D/C, rash

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Case 1 Exam

• Distressed, ill-appearing, toxic
• Febrile 102.5 P 125 BP 135/88
• No OP lesions or meningismus
• CV Reg, tachy, 2/6 sys. murmur
• Lungs CTA
• Erythemetous, tender R-wrist with effusion other
  joints negative
• No rash

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Case 1 Differential

• Bergers Bs
• Bugs
• Blood
• Birefringence

Robert Berger, MD, Professor of Rheumatology UNC
Chapel Hill
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Infectious Monarthritis

• Source
• Local or direct inoculation (trauma, surgery)
• Hematogenous spread (more common,72)
• Risk Factors IVDA, catheters, immunosuppression,
  extremes of age, underlying arthritis, prosthetic
  joints
• Knee most common (50)
• Beware endocarditis

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Septic Arthritis

• Microbiology
• Staph aureusmost common
• Strep (splenic dysfunction)
• Neisseria gonorrhea (young, sexually active)
• Gram negatives (immunocompromised, GI infection)
• Mycobacteria (immunocompromised)
• Fungus (immunocompromised)
• Lyme disease

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Gonococcal Arthritis

• Organism not isolated from routine media
• Special media (chocolate agar, Thayer-Martin)
  with bedside inoculation
• Culture all sites in DGI blood, urethra, cervix,
  skin, synovial fluid, rectum
• 80 yield with pan-culture

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Septic Arthritis Diagnosis

• Synovial fluid analysis
• Cell count (average 50 to 150k WBCs)
• Gram stain
• Fluid Culture
• Blood culture positive 50

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Synovial Fluid Analysis
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Hemarthrosis

• Predisposing Factors
• Trauma
• Anticoagulation
• Clotting disorders (e.g. hemophilia)
• Fracture

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Crystal Arthritis

• Gout monosodium urate (negatively birefringent
  crystals)
• Pseudogout calcium pyrophosphate (positively
  birefringent, smaller and harder to identify)
• Hydroxyapatite
• Calcium oxalate
• Lipid

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Case 1 Studies

• CBC WBCs 25K with 80 PMNs
• Synovial Fluid Analysis 44K WBCs with (75)
  PMNs
• Gram stain negative
• Crystal Positively birefringent crystals

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Pseudogout The Masquerader

• Knee (50) or wrist common
• May simulate septic arthritis
• Xrays may demonstrate chondorcalcinosis

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Case 1 Denouement

• Admitted to medicine
• Concern for concomitant septic arthritis
• Blood cultures and synovial cultures negative
• Patient has prompt and dramatic response to high
  dose NSAIDS
• Discharges home within 48 hours

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Case 2

• 53 yo with acute onset pain, swelling in right
  knee no prior history
• H/O HTN, obesity, diabetes, asthma
• Meds HCTZ, diltiazem, metformin, ASA, atenolol,
  ibuprofen, albuterol
• VS T 101.1 P 92 BP 152/96 173kg
• R Knee Effusion exquisite pain with movement

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Fluid Analysis
Treated with high-dose NSAIDS and sent home.
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Case 2 2nd Presentation

• Returns 2 weeks later with unrelieved pain and
  swelling.
• Knee re-tapped

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Cultures Reviewed

• Patient given single dose IV oxacillin and sent
  out with oral cephalexin

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Case 2 3rd Presentation

• Returns 3days later unimproved
• Joint culture from 3 days earlier confirm septic
  arthritis
• Admitted for septic arthritis and received IV abx
• Undergoes arthroscopic debridement, synovectomy
• Incurs substantial disability

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Crystal Arthritis Infection How Common It?

• 5/314 patients presenting to Mayo Clinic with
  joint pain had both crystal-proven CPPD and
  culture-proven septic arthritis (1.6)
• Incidence of concurrent gout and septic arthritis
  in patients presenting with monoarthritis has not
  been reported
• Review of 57 cases with both crystal arthropathy
  and septic arthritis, 43 (75) had gout septic
  arthritis, 11 (19) had CPPD septic arthritis,
  3 (5) had gout CPPD septic arthritis

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Proposed Mechanisms Whereby These 2 Diseases May
Be Linked

• Septic arthritis creates conditions (low pH)
  favoring crystal precipitation
• Septic arthritis results in production of enzymes
  that release crystals embedded in cartilage (the
  enzymatic strip mining hypothesis)
• Disruption of joint structure by crystal disease
  predisposes to bacterial seeding

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Take Home Message

• Among patients with a history of crystal
  arthropathy presenting with monoarthritis,
  concurrent septic arthritis is probably rare, but
  not rare enough to safely exclude outright
• If patient does not have history or crystal
  proven arthritis, do arthrocentesis on any hot
  joint, with priority given to crystal exam and
  culture
• Suspect other cause if condition does not respond
  to standard therapy
• Do not rely on any other tests (e.g. CBC, cell
  count, ESR) for diagnosis
• Repeat arthrocentesis for any joint failing to
  improve
• ALWAYS FOLLOW UP ON TEST RESULTS