What laboratory and imaging studies are used to diagnose relapsing polychondritis?

How to Test for Relapsing Polychondritis

The diagnosis of relapsing polychondritis is primarily clinical, supported by pulmonary function tests with flow-volume curves, CT scanning of the chest to assess airway involvement, and laboratory markers of inflammation, though no specific laboratory test is diagnostic. 1

Diagnostic Approach

Clinical Evaluation

The diagnosis rests fundamentally on recognizing the characteristic pattern of cartilage inflammation. Look specifically for:

• Auricular chondritis (88% of patients) - swelling and erythema of the ears, notably sparing the ear lobes (which lack cartilage)
• Arthralgias (81% of patients)
• Respiratory symptoms - chronic cough, wheezing, stridor, dyspnea, hoarseness, or tenderness over laryngotracheal cartilage
• Nasal chondritis - saddle nose deformity
• Ocular inflammation (57% of patients) 1, 2

A critical pitfall: Up to 25% of patients present with respiratory symptoms as their initial manifestation, and more than half have no chondritis at presentation, making early diagnosis challenging 3, 4.

Essential Diagnostic Tests

Pulmonary Function Testing:

• Perform inspiratory and expiratory flow-volume curves - this is specifically recommended to identify clinically subtle airway involvement 1
• Flow volume loop abnormalities are found in 33% of patients 2
• This test can detect early laryngotracheal involvement before it becomes clinically apparent

CT Imaging:

• Chest CT is the primary imaging modality and reveals:
  • Thickening and stenosis of tracheobronchial walls
  • Collapse and calcification of cartilage
  • Bronchiectasis in late stages 1, 5
• Abnormalities are found in 48% of patients who undergo chest CT 2
• Dynamic expiratory CT is particularly useful for assessing airway collapse 3
• Note: Chest radiographs are usually unhelpful for diagnosis 1

Advanced Imaging When Available:

• FDG-PET scan can demonstrate cartilaginous inflammation and is particularly valuable in atypical presentations where histopathology is unavailable 4, 6
• MRI can show thickening, contrast enhancement, and increased T2-signal intensity in affected cartilage 5, 3
• Imaging findings correlate better with clinical features than laboratory markers 5

Laboratory Studies

Inflammatory Markers:

• ESR, CRP, and IL-6 are typically elevated during active disease 7, 6
• C-reactive protein to albumin ratio (CAR) emerged as an independent risk factor for disease activity (OR = 4.422) with AUC of 0.758 for identifying active patients 7
• Platelet to lymphocyte ratio (PLR) and neutrophil to lymphocyte ratio (NLR) are elevated in active disease 7

Autoantibody Testing:

• Anti-type II collagen antibodies can be positive (as in the case example showing 33.9 EU/mL) 8
• However, anti-collagen type II and anti-matrilin-1 antibodies are neither sensitive nor specific and cannot be used for diagnostic purposes 3
• Consider checking ANA, RF, anti-CCP to evaluate for associated autoimmune diseases (present in one-third of patients) 3

Complete Blood Count:

• A model based on monocyte counts and NLR could distinguish RP patients from healthy controls with AUC of 0.845 7
• Lower natural killer cell levels may be present 7

Additional Investigations

Bronchoscopy:

• Shows inflammation, collapse, and stenosis of larynx, trachea, and/or bronchi
• Reveals redness and swelling of tracheal/bronchial mucosa in membranous lesions 8
• Not required for diagnosis as findings are not diagnostic of the disease 1
• Important caveat: Bronchoscopy can worsen respiratory dysfunction and should be used judiciously 3

Echocardiography:

• Abnormalities found in 48% of patients
• Recommended for monitoring large vessel involvement 2

Critical Diagnostic Considerations

When to Suspect Alternative Diagnoses:

• In older male patients with myelodysplastic syndromes, consider VEXAS syndrome (requires detection of somatic UBA1 gene mutations) 4, 9
• Rule out immune checkpoint inhibitor-related adverse events in cancer patients 9
• Consider other autoinflammatory diseases in atypical presentations 9

Diagnostic Criteria: The diagnosis can benefit from Michet's criteria (referenced but not detailed in the evidence), though clinical judgment remains paramount 3.

Key Pitfall to Avoid: Do not wait for all classic features to appear before initiating treatment. Respiratory involvement is irreversible and the major cause of morbidity and mortality, making early recognition and treatment essential 8. The disease exhibits a relapsing course in 86% of patients 1.