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Rheumatology - Undifferentiated Inflammatory Arthritis - Fast Facts | NEJM Resident 360

Inflammatory arthritis is a group of diseases that affect the joints, is characterized by an inflammatory response, and can sometimes involve an autoimmune process. There are numerous possible causes, and early in the course of illness (within the first year of presentation) an underlying diagnosis may not be immediately apparent. This specific clinical scenario may be termed “undifferentiated inflammatory arthritis.”

Many conditions can cause inflammatory arthritis, which can be categorized and include the following examples:

Evaluation

Careful history taking and a thorough physical examination will aid in the identification of extra-articular manifestations, the distribution and nature of the arthritis, and the time course of the disease process. Important aspects of history and examination include:

• distribution of joints involved and presence of joint swelling

• cutaneous, nail, and hair abnormalities (such as sclerodactyly, rash, alopecia) and their distribution

• Raynaud phenomenon

• tendon involvement

• lymphadenopathy and organomegaly

• ocular involvement

• pulmonary abnormalities

• muscle weakness of limbs, head, neck, and pharynx

• abdominal symptoms (such as hematochezia, diarrhea, and abdominal pain)

• recent travel, joint injury, or infections (including sexually transmitted infections)

The history and physical examination will then direct sensible additional investigation to include or exclude the provisional diagnoses.

Not all tests are required for all patients. Some relevant investigations might include:

Diagnostic Tests to Investigate Undifferentiated Inflammatory Arthritis

Investigation Type	Tests
Standard laboratory tests

• Complete blood examination

• Biochemistry

• Liver function tests

• C-reactive protein and erythrocyte sedimentation rate

• Urine: microscopy, culture and sensitivities, cell count, red cell morphology

• Serum angiotensin-converting enzyme

• Creatine kinase

| | Autoantibody tests |

• Rheumatoid factor

• Anti–cyclic citrullinated peptide (anti-CCP) antibodies

• Antinuclear antibodies

• Antibodies to extractable nuclear antigens

• Antineutrophil cytoplasmic antibodies (ANCAs)

| | Imaging |

• Plain radiographs of affected joints

• Chest radiograph

• Ultrasonography of affected joints

• MRI of affected joints

| | Other |

• Pulmonary function tests

• Transthoracic echocardiography

• Arthrocentesis with synovial fluid analysis (cell count with differential, gram stain, microscopy, culture and sensitivities, crystal identification by polarized microscopy)

|

Synovial fluid analysis: In certain situations, such as when septic arthritis is suspected, synovial fluid analysis is vital. Although the table below is a good guide, there is significant overlap in the synovial fluid white blood cell (WBC) count for a number of conditions; for example, septic arthritis could be present with <50,000 cells/mm³ and a noninflammatory condition (such as osteoarthritis) could exist with a synovial fluid count >2000 cells/mm³ (though rarely much more). In general, the higher the synovial fluid WBC count, the greater the concern for septic arthritis. Malignancies rarely affect the joint; as a result, synovial fluid cytology is a relatively low-yield test and should not be tested routinely.

Synovial Fluid Analysis

	Normal	Noninflammatory	Inflammatory	Septic	Hemorrhagic
Clarity	Transparent	Transparent	Translucent	Opaque	Bloodstained
Color	Clear	Yellow	Yellow	Yellow/brown	Red/xanthochromic
Viscosity	High	High	Low	Low	Variable
WBC/mm3	<200	200–2000	2000–50,000	>50,000	200–2000
PMNs (%)	<25	<25	>50	>75	50–75
Crystals	Negative	Negative	May be positive (based on underlying pathology)	Negative	Negative
Gram stain	Negative	Negative	Negative	Positive	Negative

Abbreviations: WBC, white blood cell; PMNs, polymorphonuclear neutrophils

Treatment

It is tempting to treat undifferentiated arthritis with glucocorticoids to reduce suffering, however; the underlying pathological process will likely be altered. It is preferable to defer the use of glucocorticoids until either a diagnosis is reached, investigation for the underlying cause has been completed, and infection has been ruled out. Analgesic medications that will not alter the pathology include:

• nonsteroidal anti-inflammatory drugs (NSAIDs)

• acetaminophen

• tramadol

• fish oil

• topical NSAIDs

Disease-modifying antirheumatic drugs other than glucocorticoids are generally reserved for use in select cases, such as those considered to represent early rheumatoid arthritis or spondyloarthropathy.

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