99mTechnetium pyrophosphate scintigraphy in the detection of skeletal muscle disease

Cardioprotective Effect of Paricalcitol on Amitriptyline-Induced Cardiotoxicity in Rats: Comparison of [99mTc]PYP Cardiac Scintigraphy with Electrocardiographic and Biochemical Findings

Taking an overdose of AMT, a commonly prescribed tricyclic antidepressant drug, has an increased risk of sudden cardiac death. The cardiotoxicity of amitriptyline (AMT) is a commonly observed toxicity with high morbidity and mortality rates in emergency departments (ED). Nevertheless, there are still no effective treatment options for AMT-induced cardiotoxicity. The aim of the present study was to evaluate the effects of paricalcitol (PRC), a Vitamin D receptor agonist, using electrocardiographic (ECG), biochemical, and scintigraphic methods. Twenty-eight male Wistar rats were randomly divided into four groups: untreated control (CON), amitriptyline-induced cardiotoxicity (AMT), paricalcitol (PRC), and amitriptyline + paricalcitol (AMT + PRC). Cardiotoxicity was induced by intraperitoneal (i.p) injection of a single-dose AMT (100 mg/kg). PRC was administered as 10 μg/kg (i.p.) after the injection of AMT. We examined ECG, biochemical, and scintigraphic results of PRC administration on AMT-induced changes. Cardiotoxicity of AMT was characterized by conduction abnormalities (increased QRS complex, T wave, and QT interval duration and elevation of ST segment amplitude), elevated ^99mTechnetium Pyrophosphate ([^99mTc]PYP) uptake, and increased cardiac troponin T (cTnT) levels. Treatment with PRC significantly decreased all AMT-associated conduction abnormalities in ECG (p < 0.001), and decreased [^99mTc]PYP uptake (p < 0.001) and serum cTnT level (p < 0.001). The present study indicated that the vitamin D receptor agonist paricalcitol could decrease the AMT-induced cardiotoxicity. This suggests [^99mTc]PYP as a non-invasive method for the evaluation of myocardial injury induced by AMT. According to the results of the present study, PRC has beneficial effects on AMT-induced cardiotoxicity.

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

BACKGROUND

Nuclear imaging is increasingly being used in the diagnostic work-up of idiopathic inflammatory myopathy (IIM). Increased muscular uptake of technetium-99m-pyrophosphate (^99mTc-PYP) has hitherto been assessed qualitatively by planar scintigraphy. We set out to perform quantitative tomographic scintigraphy in IIM.

RESULTS

Ninety IIM patients and 48 control subjects underwent ^99mTc-PYP single-photon emission computed tomography (SPECT)/CT of the upper and lower body. Scans were evaluated visually by an intensity score (1-4) and quantitatively by the mean standardized uptake value (SUV_mean) in thigh muscles after semi-automated segmentation of these. Furthermore, a SUV_mean gradient down along the thighs was determined by linear regression of the slice-by-slice activity. Interobserver analyses were performed on qualitative evaluations. Compared to controls, patients more often had a high intensity score (p < 0.0001), but interobserver analyses revealed only moderate agreement. The thigh muscular ^99mTc-PYP activity (SUV_mean) was 60% higher in patients than in controls, p < 0.0001, albeit with a wide range. There was an activity gradient down the thigh muscle, the proximal tracer uptake being highest, and this gradient was steeper in patients than in controls; the activity decreased by 0.00024 and 0.00010 SUV_mean mm^-1, respectively, along the thighs.

CONCLUSIONS

The muscular uptake of ^99mTc-PYP was significantly higher in patients than in healthy controls by qualitative and quantitative assessment. The tracer uptake was higher in the proximal than in the distal part of the thigh muscle, and SUV_mean gradients differed between groups. Hence, tomographic nuclear imaging allowing for quantification of the ^99mTc-PYP uptake might contribute to the diagnosis of IIM, and SPECT/CT of the lower body might suffice.

Role of bone scan in the assessment of polymyositis/dermatomyositis

The aim of this study was to determine the significance of bone scan findings in Korean polymyositis/dermatomyositis (PM/DM) patients. The participants in this study were 26 PM/DM patients who fulfilled the proposed criteria for definite or probable PM/DM. All patients had been examined by bone scan. The results were analyzed visually and quantitatively using the uptake ratios. Correlations between the bone scan parameters of six proximal muscle groups (trapezius, deltoid, biceps, iliopsoas, quadriceps, and gluteus medius and maximus) and clinical parameters (laboratory values and manual muscle test) representing disease activities were assessed. Based on visual analyses of their bone scans, 10 of 14 (71.4 %) patients with active PM/DM had abnormal muscle uptake. Visual grading of the bone scans had a sensitivity and specificity of 74 and 90.9 %, respectively, for the assessment of muscle inflammation. Maximal proximal muscle uptake ratios, as determined on the bone scans, were significantly higher in patients with active PM/DM than in those with inactive disease (median 1.97 vs. 1.02, p = 0.046). Maximal proximal uptake ratios correlated significantly with creatine kinase (r = 0.394, p = 0.046), lactate dehydrogenase (LDH, r = 0.473, p = 0.015), aldolase (r = 0.428, p = 0.029), erythrocyte sedimentation rate (r = 0.412, p = 0.036), C-reactive protein (r = 0.454, p = 0.002), and manual muscle test results (r = -0.399, p = 0.044). Mean proximal muscle uptake ratios correlated significantly with LDH (r = 0.438, p = 0.025) and aldolase (r = 0.572, p = 0.002). Visually assessed proximal muscle uptake grades and maximal proximal muscle uptake ratios as determined by bone scan correlated significantly with the levels of known PM/DM disease activity markers. The findings of this study suggest that bone scan is a useful imaging technique for the evaluation of PM/DM patients.

Postinfectious focal necrotizing myopathy

A 37-year-old woman was admitted to our department with general fatigue, fever, and asymmetric pain in her lower legs, 2 weeks after a common cold. Dynamic skeletal scintigraphy with 780 MBq (20 mCi) Tc-99m HDP revealed increased perfusion and tracer uptake in the soft tissue of the lower legs, suggesting an inflammatory etiology. A muscle biopsy revealed a vasculitic necrotizing myopathy predominantly affecting the small vessels of the lower legs. We diagnosed it as a postinfectious immunologic reaction.