Dialysis Related Amyloid Arthropathy on ¹⁸FDG PET-CT

Editor,

A 60 year-old male patient with end stage kidney disease secondary to Alport syndrome presented with worsening swelling and pain in both shoulders. He had been on regular haemodialysis for 20 years, having had two failed renal transplants previously and had renal amyloidosis confirmed on renal biopsy. Radiographs of the shoulders showed evidence of an erosive arthropathy affecting the glenohumeral and acromioclavicular joints without significant degenerative change (Figure 1). In view of advanced renal failure and contraindication to MRI, a PET-CT scan was performed with 18-fluorodeoxyglucose (¹⁸FDG) to assess for amyloid involvement in the shoulders. This demonstrated periarticular radiotracer uptake in both shoulder joints with greater involvement on the left, compatible with bilateral amyloid arthropathy in the shoulder joints (Figure 2).

Fig 1.

Anteroposterior radiograph of the right shoulder showing erosions affecting the coracoid process, humeral head and acromioclavicular joints. The glenohumeral joint space is preserved with no subchondral cystic change present.

Fig 2.

(A) Fused axial 18FDG-PET/CT image demonstrating periarticular radiotracer uptake in both shoulder joints with greater involvement on the left. (B) Coronal maximum-intensity projection 18FDG-PET/CT attenuation corrected image demonstrating FDG uptake in the periarticular regions (arrows) consistent with amyloid arthropathy.

Amyloidosis is characterised by extracellular deposition of protein and protein derivatives. The disease becomes clinically significant when its diffuse form affects organ function or when local deposition creates a mass. Our patient had dialysis-related amyloidosis (DRA) which is a well recognized complication in patients on long-term dialysis.^{1, 2} Amyloid deposition with p2-microglobulin has high affinity for collagen and predominantly affects the osteoarticular system.^{3, 4} DRA is clinically manifested by an erosive and destructive osteoarthropathy particularly in the form of scapulohumeral periarthritis, carpal tunnel syndrome, bone cysts, spondyloarthropathy and pathologic fractures.¹ As histopathological confirmation is not always possible and because increased serum p2-microglobulin levels are not diagnostic, the diagnosis is often made by imaging. Diagnosis is essential to prevent more serious complications such as pathologic fractures.

Plain radiography may demonstrate advanced DRA findings such as bone erosions and cystic lesions, but it is not sensitive in the demonstration of early changes and can also underestimate the extent of the disease. Ultrasound can be helpful in the detection of amyloid deposition in the periarticular soft tissues. CT and MRI are useful for the detection of lesions especially in the non-axial skeleton.^{1, 3} On MRI, amyloid arthropathy typically demonstrates homogenous low-to-intermediate signal intensity on both T1 and T2-weighted images, and there can be high T2 signal in areas of cystic change. Periarticular amyloid may enhance mildly after gadolinium administration.^{5, 6} However, the administration of gadolinium has been linked to the development of nephrogenic systemic fibrosis in patients with advanced renal failure, in particular patients on dialysis and is contraindicated in this patient group.

PET-CT with ¹⁸FDG has been reported to be a useful imaging modality to demonstrate areas of systemic amyloid deposition. Cases of amyloid arthropathy in patients with multiple myeloma and light-chain amyloidosis diagnosed with ¹⁸FDG PET-CT have been described.^{7, 8} Our case complements these reports in showing the utility of ¹⁸FDG PET-CT in the diagnosis of amyloid arthropathy secondary to DRA, which is particularly useful in this patient population due to the contraindication to gadolinium which renders MRI evaluation suboptimal. ¹⁸FDG PET-CT represents a non-invasive imaging modality which can be of value when conventional radiographs are not helpful in establishing the diagnosis or when disease extent is underestimated in patients with suspected amyloid arthropathy.