Quantitative 3D scintigraphy shows increased muscular uptake of pyrophosphate in idiopathic inflammatory myopathy

Acute Exacerbation of Idiopathic Pulmonary Fibrosis With Concurrent Cardiac Amyloidosis: A Technetium Pyrophosphate Study

Amyloidosis presents a diagnostic challenge, particularly when concomitant with severe conditions like acute exacerbations of idiopathic pulmonary fibrosis (IPF). In this report, we detail the case of a 73-year-old patient with acute exacerbation of IPF and simultaneous emergence of cardiac amyloidosis. The patient's clinical journey began with persistent exertional dyspnea, progressing to hypoxemia on admission. Chest CT scans showed extensive ground-glass opacities, consolidations, and pre-existing honeycombing-like cysts and reticular shadows, accompanied by a right-sided pleural effusion. The therapeutic strategy for acute exacerbation of IPF encompassed methylprednisolone pulse therapy, tacrolimus, and nintedanib, augmented with intravenous immunoglobulin and recombinant thrombomodulin. Concurrently, heart failure with preserved ejection fraction was managed with a pharmacological trio: empagliflozin, diuretics, and eplerenone. A hypertrophied heart and low limb voltage prompted an investigation for cardiac amyloidosis, which 99mTechnetium pyrophosphate (99mTc-PYP) scintigraphy confirmed, yielding a probable diagnosis. Following steroid tapering, the patient was discharged home. This case prompted an investigation into the potential role of amyloidosis in pulmonary pathology. Our retrospective review of 10 patients, including four with cardiac amyloidosis, who underwent 99mTc-PYP scintigraphy, revealed a nonsignificant yet notable trend of increased pulmonary accumulation in cardiac amyloidosis cases (median (interquartile range): 5.4×104 (5.3-13.1×104) vs. 3.6×104 (2.4-5.1×104), p=0.0667). Notably, the pulmonary counts in this patient exceeded the negative cohort's mean values, hinting at a possible contribution of amyloid deposition to pulmonary pathology. This study, pioneering in evaluating lung field accumulation of 99mTc-PYP in cardiac amyloidosis, may provide novel insights into the influence of amyloidosis on pulmonary conditions.

Treatment-naïve idiopathic inflammatory myopathy: disease evaluation by fluorodeoxyglucose versus pyrophosphate

Background

Imaging of idiopathic inflammatory myopathies (IIMs) is challenging, and no pathognomonic signs exist. Different tracers have been tested for this purpose, mainly inflammation markers including technetium-99m-pyrophosphate (PYP). We aimed to examine the utility of fluorine-18-fluorodeoxyglucose (FDG) relative to PYP in idiopathic inflammatory myopathy (IIM).

Methods

Using visual grading and CT-guided muscular segmentation and standardized uptake values (SUVs), we assessed muscular tracer uptake qualitatively and quantitatively, comparing FDG uptake in eight patients with recent-onset IIM and 24 healthy control persons and FDG and PYP uptake in seven patients.

Results

Muscular FDG and PYP uptake was increased in all patients. However, uptake distribution and signal intensity differed considerably. FDG scans revealed clear involvement of certain muscle groups including core and swallowing muscles and, in addition, abnormality in diseased extra-muscular organs. PYP was mainly visible in bones, whereas muscular PYP uptake was generally discrete and primarily located in the extremities. Quantitatively, FDG uptake was significantly higher in patients than in controls; the volume-weighted SUVmean for all right-side muscles was 0.84 versus 0.60 g/ml (95% confidence interval (CI) for mean difference 0.14–0.34, p = 0.0001). FDG SUVmean values were up to four times higher than PYP mean values in upper limb muscles (95% CI for the mean ratio 2.37–3.77, p = 0.0004) and two–three times higher in lower limb muscles (95% CI for the mean ratio 2.28–2.71, p < 0.0001).

Conclusions

Muscular FDG uptake was higher in treatment-naïve IIM patients than in healthy controls and more distinct than PYP uptake in patients with a potential to reveal extra-muscular IIM involvement and malignancy. Thus, FDG appears to be superior to PYP in the diagnostic evaluation of IIM.

Advances in Quantitative Imaging of Genetic and Acquired Myopathies: Clinical Applications and Perspectives

In the last years, magnetic resonance imaging (MRI) has become fundamental for the diagnosis and monitoring of myopathies given its ability to show the severity and distribution of pathology, to identify specific patterns of damage distribution and to properly interpret a number of genetic variants. The advances in MR techniques and post-processing software solutions have greatly expanded the potential to assess pathological changes in muscle diseases, and more specifically of myopathies; a number of features can be studied and quantified, ranging from composition, architecture, mechanical properties, perfusion, and function, leading to what is known as quantitative MRI (qMRI). Such techniques can effectively provide a variety of information beyond what can be seen and assessed by conventional MR imaging; their development and application in clinical practice can play an important role in the diagnostic process and in assessing disease course and treatment response. In this review, we briefly discuss the current role of muscle MRI in diagnosing muscle diseases and describe in detail the potential and perspectives of the application of advanced qMRI techniques in this field.