- Design
- systematic review and meta-analysis of three observational studies, four databases searched to April 2025
- Population
- 97 patients with suspected relapsing polychondritis who underwent 18F-FDG PET/CT
- Primary outcome
- pooled PET positivity rate
- Effect
- 94% (95% CI 73-99%), I-squared 0%; pooled baseline SUVmax 4.0 (3.5-4.6)
Relapsing polychondritis is rare, hard to confirm and dangerous when it reaches the airway, and there is no agreed role for imaging. A systematic review searched four databases to April 2025 and found three studies with 97 patients between them reporting an FDG PET/CT positivity rate in suspected relapsing polychondritis.
The pooled positivity rate was 94% (95% CI 73-99%), with no heterogeneity between the three studies, and a pooled baseline SUVmax of 4.0 (3.5-4.6). PET picked up cartilage involvement in more than a quarter of patients at sites that were not causing symptoms, and did better than clinical assessment at inaccessible sites such as the peripheral airways. PET parameters tracked inflammatory markers.
The important caveat is what a positivity rate is not. These studies enrolled patients in whom the diagnosis was already suspected and reported how often the scan lit up — that is not sensitivity, and without patients who turned out to have something else there is no specificity at all. So this cannot tell you how often FDG PET is positive in a mimic. Where it is genuinely useful is mapping: in a patient with an established diagnosis, PET can show airway and costal involvement that examination misses, and can be repeated to judge treatment. Availability and cost make that a decision to take deliberately in Indian practice, not a routine addition.
- Consider FDG PET/CT for mapping extent in confirmed relapsing polychondritis, not for making the diagnosis
- Asymptomatic airway involvement was found in more than a quarter — worth knowing before an anaesthetic
- A positive scan does not exclude infection, malignancy or IgG4-related disease
- Pair imaging with dedicated airway assessment where symptoms suggest tracheobronchial disease
- Cost and access make this a considered request in India rather than a first-line test
The statistics, in plain English
A pooled rate of 94% with a confidence interval from 73% to 99% rests on three studies and 97 patients; the width of that interval, not the point estimate, is the honest summary. I-squared of 0% means the three studies agreed with each other, which is reassuring about consistency but says nothing about whether all three shared the same selection bias. Because no control group without relapsing polychondritis was included, specificity is unmeasured and the test's ability to distinguish mimics is unknown.
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