¹⁸FDG PET/CT in a Case of Relapsing Polychondritis

INTRODUCTION

Relapsing polychondritis is a rare autoimmune disorder characterised by recurrent inflammation and progressive destruction of cartilage commonly involving auricular, nasal and tracheobtonchial structures^[1]and often presents with non-specific respiratory symptoms leading to delayed diagnosis. FDG PET-CT showing uptake in the involved regions serves as a valuable tool for early diagnosis,whole body disease mapping and guiding appropriate biopsy and therapy.

CASE REPORT

A 22-year-old female presented with a stridor. She also has a 2-month history of dyspnea, persistent cough with sputum, and wheezing and a 10-day history of low-grade fever. On examination, she was found to have subglottic stenosis. She underwent an emergency tracheostomy procedure to relieve the stridor. Further, her blood investigations showed elevated inflammatory markers (ESR: 40 mm/h) and she did not respond to steroids and disease modifying antirheumatic drugs, however responded to cyclophosphamide.

Histopathological examination of the tissue from the subglottic stenotic lesion showed nonspecific features of mild chronic inflammation in the strips of mucosa and edema in the lamina propria. ¹⁸F-FDG PET/CT was done to help uncover the underlying pathology [Fig 1].

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Fig 1:

(a) Maximum intensity projection image shows increased metabolism in the glottic and infraglottic airways (blue arrow) and focal hypermetabolism in the xiphisternal region (green arrow) localized to the cartilage. (b) Sagittal fused PET/CT image showing focal hypermetabolism in the xiphisternal region (green arrow). (c and d) Axial CT and fused PET/CT image showing a hypermetabolic stenotic lesion in the subglottic region (blue arrow) causing narrowing of the airway. (e, f and g) Various axial fused PET/CT images showing focal hypermetabolism in the thickened cartilages of the tracheobronchial tree (blue arrow in f)in the xiphisternal region (green arrow in g) (h) Coronal fused PET/CT image showing hypermetabolism in the thickened cartilages of the tracheobronchial tree (blue arrow)

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Maximum-intensity projection image (a) shows increased metabolism in the glottic and infraglottic airways (blue arrow) and focal hypermetabolism in the xiphi-sternal region-localized to the cartilage (green arrow, also seen in sagittal image b and axial image h). Axial images (c- fused PET/CT and d- CT)- show a hypermetabolic stenotic lesion in the subglottic region causing severe narrowing of the airway. Coronal (f) and axial (g) images show hypermetabolism in the thickened cartilages of the tracheobronchial tree.

PET/CT revealed the pattern of increased metabolism in the cartilages of the glottis, tracheobronchial tree, and xiphisternum, suggestive of inflammatory etiology-likely relapsing polychondritis (RP). The diagnosis of RP was made based on the clinical, pathological, and characteristic ¹⁸F-fluoro-deoxy-glucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) findings.

DISCUSSION

RP (Orpha 728) is a rare, chronic, autoimmune, and inflammatory disorder that primarily affects cartilage, exhibiting an intermittent course mediated by an autoimmune reaction to type II collagen,^[1] which is abundant in cartilage including the ear, nose, airway, and the sclera.^[2] It presents with nonspecific symptoms of airway involvement that are commonly misdiagnosed prima facie with hyperreactive airway disease, amyloidosis, or chronic bronchitis and follows an indolent relapsing-remitting course, sometimes causing destruction of tracheobronchial cartilage requiring a tracheostomy or tracheoplasty.^[3]

Various criteria, including McAdam, Damiani, and Levine, Michet’s, are being commonly used for the diagnosis which is based on clinical findings, cartilage biopsies, and response to steroids.^[4] Chest CT and pulmonary function tests are the initial modalities for the detection of airway involvement but suffer from low sensitivity and specificity^[5] 18F-FDG PET/CT can be used to identify the multisystem involvement patterns and extent of the disease and identify the sites of biopsy. The ability of FDG PET/CT to detect disease sites is based on the uptake of the radioactive FDG by newly formed granulation tissue and macrophages in the inflammatory process.^[6,7] Further, modified Michet’s criteria include FDG PET/CT findings are a supporting evidence in addition to clinical findings and Lei et al. described the presence of two or more symmetrically distributed cartilages or joints with high-¹⁸F-FDG-uptake lesions strongly indicates RP, like in this case.^[8,9]

CONSLUSION

As demonstrated in our case, 18FDG PET/CT is useful to identify the disease involvement and also for early intervention which prevents irreversible cartilage damage.