“Relapsing Polychondritis Revisited: Enhanced Lesion Detection with Ga-68 FAPI PET/CT over F-18 FDG PET/CT”

A 50-year-old female presented with complaints of hoarseness of voice and throat pain. She also complained of fever, lower limb joint pain and ringing sensation in the right ear for one month. ESR (Erythrocyte Sedimentation Rate) and CRP (C-Reactive Protein) were elevated, IgG4 levels were normal, and ANA (Anti-Nuclear Antibody) by Immunofluorescence was weakly positive. Bronchoscopy showed subglottic stenosis, diffuse circumferential thickening of the trachea, causing ~ 70% luminal narrowing. An endotracheal biopsy was taken that showed mild nonspecific inflammation. Initially, the patient was referred for FDG PET/CT to look for any airway inflammation, multisystem involvement and for possible differential diagnoses.^[1] In addition to FDG PET/ CT, a Ga-68 FAPI PET/CT^[2,3] was performed for academic and investigational purposes to assess the extent of fibroblast activation and potential subclinical involvement [Fig 1].^[4]

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Fig 1:

(a) Maximum Intensity Projection image (MIP), (b,c) fused axial and (d) sagittal (e,f,g) images of F-18 FDG PET/CT and corresponding CT images revealed hypo enhancing wall thickening involving cartilaginous area of entire trachea (green arrow in d) (h,i) bilateral main bronchi with associated luminal narrowing and relative sparing of posterior membrane. Fused axial and (j) sagittal and MIP (k) images of Ga-68 FAPI PET/CT and (e,f,g) corresponding CT images established increased extent of disease involvement, including the entire trachea (yellow arrow in j), bilateral bronchi, bilateral aryepiglottic folds (white arrow in h) and multiple bilateral anterior costal cartilages (dotted red arrow in i).

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Given FAP expressions in inflammatory and reparative processes, Ga-68 FAPI imaging thus offers superior sensitivity for the detection and characterisation of chronic inflammatory aetiologies like relapsing polychondritis.^[5-7]