Monoarticular / Oligoarticular Arthritis

Last posting we discussed a general approach to joint pain, & specifically Bilateral Small-Joint Polyarthritis.  today we’ll address…

Differential Diagnosis  —  Mono- / Oligoarticular Arthritis

More Common


Before delving in, a word about the uncommon but worst-case scenario — acute onset new Monoarticular Arthritis which might be a Septic Joint.  If suspicious, an E.D. can perform arthrocentesis and get results stat, start IV antibiotics pending results, and admit if cell counts of joint fluid are suggestive (to continue treatment cultures return).

Knee taps are easy; other  joints depend on the skills and interests of clinicians.  For the hip, experienced interventional radiologists use fluoroscopy or ultrasound [certainly the latter in children].  So have a decent index of suspicion.

Most patients with septic arthritis are febrile (except the very old).  The joint usually looks swollen / feels warm.  Generalized malaise raises the likelihood.

The vast majority have a risk factor:

            •  Age >80                   •  Rheumatoid Arthritis          •  Prosthetic Joint
            •  Skin Infection          •  Injection Drug Use / Alcoholism
  •  Recent joint surgery or steroid injection            •  Diabetes              

 A young woman may have Disseminated Gonorrhea, especially if symptoms began shortly after menses.  This occurs most commonly in the knee, followed by ankle and wrist.  Culture joint fluid if possible, also blood, and especially cervix, rectum, and/or pharynx (depending on sex practices; patients are commonly asymptomatic at portal of entry).  Diagnosis is often made by response to empiric treatment, since cultures may well be negative.

Certainly, take a good history: if the patient remembers prior episodes of similar symptoms, perhaps in another joint, we’re probably not dealing with new onset.  The only caveat is that joints injured from long-standing rheumatoid arthritis are prone to infection; also those with gout, pseudogout, osteoarthritis, and psoriatic arthritis.


Be sure you’re not dealing with periarticular conditions such as bursitis or tendonitis.  See our prior posting Musculoskeletal Pain for  distinguishing among musculoskeletal structures.  But basically —  Confirm joint involvement by eliciting Tenderness With Passive ROM:

  • With patient well-relaxed, support the limb, and gently wiggle the joint.
  • Wiggle it more.
  • If the examiner can move the joint through some ROMs, joint synovitis is very unlikely.
  • Needn’t be full ROM.  For example, a swollen knee will hurt with flexion due to simple pressure.  But if subsequent full passive extension is non-tender, it’s not joint.

CAUTION:  Red, hot, swollen, tender “joint” may be a cellulitis [not something you want to advance a needle through en route to sterile synovium].

  • Perform the same maneuver above to confirm it’s joint.  With cellulitis, stretching the skin in one direction may be tender, but not the opposite ROM.
  • Lightly palpate and wiggle the skin: if that’s tender, the infection is likely dermal.
  • Septic hips may be too deep to be red / hot.

Inquire about TRAUMA.  If a patient who awakens with monoarticular joint swelling happened to be drunk or high the night before, they may not remember the injury.

Suspect HEMARTHROSIS in patient on anticoagulants, with sickle cell, or another clotting disorder.

Back to Arthritis

From now on, let’s say we’re dealing with bona fide Monoarticular or Oligoarticular Arthritis.  And we’ve decided the patient doesn’t have a septic joint.  Once again, the main causes:

More Common


I personally wind up sending most of my arthritis patients to Rheumatology, because:

  1. They’re best at diagnosis, since there are no true gold standards for most of these diseases; and
  2. I’m not comfortable managing treatment such as tumor necrosis factor inhibitors and other DMARDs (Disease-Modifying Anti-Rheumatic Drugs).

Gout is the one condition I’m usually OK with.  But regardless of how comfortable you do / don’t feel, it’s always challenging to try and nail the diagnosis.

Specific Joint Involvement may guide us for Monoarticular Arthritis:

KNEE  —  Tap this, because it’s easy, & a common location for Gout or Pseudogout.  Send fluid for:

  • Cell counts & Differential — Get results ASAP, because if heading toward 100,000 WBCs, or >75% PMNs, assume you missed a septic joint.
  • Crystals  —  Distinguish Gout from Pseudogout from Neither by a polarizing microscope (distinguishing crystals / absence thereof).
  • Gram Stain & Culture —  Would be really bad not to obtain these if it wound up having been infected.

1st TOE (MTP)  —  “Podagra.”  Tap if able, to look for crystals pathognomonic of Gout, but neither I nor most clinicians can or do.  So we treat empirically for Gout, and order a serum Uric Acid.  However:

  • Many people who’ll never get gout have a high uric acid
  • Up to 40% of sufferers may have a normal uric acid during an attack
  • Best time to obtain the uric acid is >2 weeks after the attack has completely subsided

A typical attack of Gout lasts around a week, resolves on its own, & eventually recurs.  Most common joints initially are 1st MTP, knee, perhaps ankle.  Any other pattern of “gout” should make you question the diagnosis (unless the gout has become chronic).

ANKLE  —  Same as 1st Toe.  Bilateral ankle arthritis suggests Sarcoidosis.
  • Order a Chest X-ray for hilar adenopathy

Lab Tests

Order the same tests you would for polyarthritis, because occasionally those conditions present with only one or few joints involved:

  • ESR / CRP
  • RF, CCP, ANA
  • HBsAg, HepC Antibody
  • CBC, U/A, Renal Function
  • Uric Acid as well

Order joint X-rays:

  • Pseudogout has diagnostic findings that the radiologist will mention
  • Erosions are very important, since they a) narrow the diagnosis, and b) will destroy the joint if we don’t Dx & Tx appropriately

Seek Clinical Clues

For oligoarthritis, or monoarticular arthritis of hip or upper extremities, the above tests may not help.  Even the ESR / CRP may be normal.  So we have to seek other clinical clues.  Most of the diseases in our differential commonly cause arthritis / arthralgias, but may be more well-known for other symptoms.

**  History of Flares  —  Patterns & duration of recurrences are key:
  • Monoarticular inflammation of 1st Toe, lasting 1-2 wks: Gout
  • Same for knee:  Gout or Pseudogout
  • Behcet’s Syndrome: arthritis flares with oral / genital ulcers, lasts 1-3 weeks
  • Late Lyme Arthritis may occur intermittently (esp. the knee)
**  Psoriasis  —  In 85% of people with Psoriatic Arthritis, skin involvement precedes joint.  Sometimes the patient may not realize it.  Look for psoriatic plaques on the extensor elbows & knees, scalp (esp. hairline), Achilles tendon, and sacrum.  If you see psoriasis, you’ll have clinched the Dx if you also find any of the following:
  • DIP arthritis in the fingers
  • Nail pits
  • Dactylitis (“Sausage Digits”)  [also with Reactive Arthritis & Sarcoid]

Nail Pits




**  Age >65 at Onset  —  think of Pseudogout and
Osteoarthritis (OA), which may mimic each other:
  • Both commonly involve the knee
  • Pseudogout may present as intermittent flares
  • Think Pseudogout in joints where OA is very unusual (hand MCPs, wrists, elbows, shoulders)
**  Oral / Genital Ulcers  —  It’s undoubtedly Behçet’s Syndrome
  • Arthritis tends to occur during ulcer flares
  • Medium joints:  knees, ankles, wrists
  • Turkish descent, or ancestors from the “Silk Road” (Arabic Peninsula on through Iran & the Indian subcontinent, to China-Korea-Japan)
**  Hx of Diarrhea (chronic / bloody)  —  think Inflammatory Bowel Disease
  • Arthritis / Arthralgias tends to occur early in disease
**  Recent Bacterial Diarrheal Infection or Genital Chlamydia  —  think Reactive Arthritis
  • Infection days to weeks before arthritis
  • Large / medium joints usually
  • Enthesitis — swelling at heel
  • Keratoderma blennorrhagica — thick, scaly plaques palms / soles
**  Lived in Lyme Disease area  —  think Late Lyme Disease
  • Objective swelling (knee, shoulder, ankle, elbow, wrist, TMJ)
  • <5 joints; NOT symmetrical
  • Hx attacks lasting weeks – months
  • Positive Serology for IgG antibody [ELISA plus Western Blot]
**  Eye Disease (iritis, uveitis, episcleritis, Scleritis)  — Think various arthritides:
  • Reactive Arthritis
  • Psoriatic Arthritis
  • Behçet’s Syndrome
  • Sarcoidosis
**  Dactylitis (“sausage digits,” see pix above)  —  think:
  • Reactive Arthritis
  • Psoriatic Arthritis
  • Sarcoidosis (chronic)
**  Enthesitis  (inflammation of tendon/ligament insertion points)  [esp. heel]  —  think:
  • Reactive Arthritis
  • Psoriatic Arthritis
**  Erythema Nodosum  (painful red nodules on shins)  —  think:
  • Reactive Arthritis
  • Sarcoidosis (acute)
  • Behçet’s Syndrome
**  Episodic Fevers (lasting ≥1 week)  —  think Still’s Disease
  • salmon-colored maculopapular rash may come & go during fevers

Osteoarthritis (Degenerative Joint Disease)  —  well, this is the most common of all.  It occurs in the relatively-elderly, onset is insidious, X-Rays show joint space narrowing, other studies are all negative.

Typical joints are hip, knee, fingers (PIP’s & DIP’s, not MCP’s), wrist (where 1st MCP meets carpal bones), feet (1st MTP and subtalar joint), and spine.  Other patterns should make you question the Dx.

These patients go to Ortho, not Rheum, but only when they’re interested in knee or hip surgery.  However, I can recall 2 interesting patients:

A 54-year-old woman came to me from Ortho for a pre-op H&P for knee replacement.  Such severe DJD seemed strange for 54, worth a few more tests.  Her ANA came back 1:320, Rheum diagnosed Limited Scleroderma [& Ortho still fixed her knee].

A 68-year-old woman developed acute onset knee pain & swelling in Mexico.  By the time she returned, it clearly wasn’t septic [she’d have died].  Work-up was negative, Ortho replaced it.  DJD it was, because her other knee (totally asymptomatic) looked almost as bad on X-ray.  Serologies all negative.

And that’s it for Arthritis (or “Arthur-itis,” as some folks say).

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