Acute Monoarthritis

Most common diagnoses in primary care:  osteoarthritis, gout and trauma.

Do not miss disorder:  septic arthritis.  Missed diagnosis can lead to sepsis, bacteremia, joint destruction or death.

Focal bone pain or recent trauma requires X-ray imaging:  must rule out metabolic bone disease, tumor or fracture.

Joint effusion with any sign of infection (redness, warmth, fever) –> tap the joint!  Do NOT base treatment solely on lab results (e.g., uric acid).  Do NOT start antibiotics prior to arthrocentesis, nor fail to start antibiotics after arthrocentesis.

DDx:

Common

Avascular necrosis

Crystals

Calcium oxalate

Calcium pyrophosphate dihydrate (pseudogout)

Hydroxyapatite

Monosodium urate (gout)

Hemarthrosis

Infectious arthritis

Bacteria

Fungi

Lyme disease

Mycobacteria

Virus

Internal derangement

Osteoarthritis

Osteomyelitis

Overuse

Trauma

Less common

Ankylosing spondylitis

Bone malignancies

Bowel disease–associated arthritis

Hemoglobinopathies

Juvenile rheumatoid arthritis

Loose body

Psoriatic arthritis

Reactive arthritis

Rheumatoid arthritis

Sarcoidosis

Systemic lupus erythematosus

Rare

Amyloidosis

Behçet syndrome

Familial Mediterranean fever

Foreign-body synovitis

Hypertrophic pulmonary osteoarthropathy

Intermittent hydrarthrosis

Pigmented villonodular synovitis

Relapsing polychondritis

Synovial metastasis

Synovioma

Systemic onset juvenile idiopathic arthritis (Still disease)

Vasculitic syndromes

Gout: needle-like uric acid crystals on microscopy.

Pseudogout:  polymorphic crystals on microscopy.

FLOWCHART FOR MONOARTHRITIS:

monoarthritis flowchart.gif

Gonococcal arthritis is the most common type of non-traumatic monoarthritis in young, sexually-active young adults.

Most important risk factors for septic arthritis:  prosthetic joint, skin infection, joint surgery, RA, age > 80, diabetes, renal disease.

  • Monoarthritis in persons with 1+ risk above: 10% chance of septic arthritis.
  • Must start abx immediately after arthrocentesis!  Most common source of bacteremia in these cases is hematogenous spread from the joint.

Axial skeletal inflammation with a single joint involved suggests a spondyloarthropathy – ask about enthesopathy or dactylitis.  Some can have uveitis or urethritis as well.

Associated skin conditions and a family history suggest psoriatic arthritis.

DIAGNOSTIC RULE FOR GOUT WHEN NO SYNOVIAL FLUID:

Diagnostic Rule for Gout When Synovial Fluid Analysis Is Unavailable

Patient with monoarthritis


Male sex

2 points

Previous patient-reported arthritis attack

2 points

Onset within 1 day

0.5 point

Joint redness

1 point

Involvement of first metatarsophalangeal joint

2.5 points

Hypertension or ≥ 1 cardiovascular diseases*

1.5 points

Serum uric acid > 5.88 mg per dL (350 μmol per L)

3.5 points

Total score:

________


≤ 4 points

> 4 and < 8 points

≥ 8 points


Non-gout in 95%

Uncertain diagnosis

Gout in 87%

Consider alternative diagnosis, such as CPPD arthritis, reactive arthritis, septic arthritis, rheumatoid arthritis, osteoarthritis, or psoriatic arthritis

Perform arthrocentesis and analysis with polarization microscopy for the presence of crystals; if not possible or available, then extensive follow-up of the patient

Manage the patient as having gout, including care for cardiovascular risk

Septic arthritis:  Fluid WBC > 50K with 90% PMNs.  Staph and strep most common causes, associated with IV drug abuse – also consider cellulitis, endocarditis, and chronic osteomyelitis.

  • Gram negative organisms: 10-21%
  • Fungal and mycobacterial in immunocompromised
  • Lyme in those at risk for exposure

Fluid WBC < 2K – osteoarthritis or internal derangement.

ESR and CRP are non-specific and cannot differentiate between inflammatory and infectious causes.

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