Statin induced myopathy does not show up in MIBI scintigraphy

Drug-induced cardiomyopathy: Characterization of a rat model by [18F]FDG/PET and [99mTc]MIBI/SPECT

BACKGROUND

Drug-induced cardiomyopathy is a significant medical problem. Clinical diagnosis of myocardial injury is based on initial electrocardiogram, levels of circulating biomarkers, and perfusion imaging with single photon emission computed tomography (SPECT). Positron emission tomography (PET) is an alternative imaging modality that provides better resolution and sensitivity than SPECT, improves diagnostic accuracy, and allows therapeutic monitoring. The objective of this study was to assess the detection of drug-induced cardiomyopathy by PET using 2-deoxy-2-[18F]fluoro-D-glucose (FDG) and compare it with the conventional SPECT technique with [99mTc]-Sestamibi (MIBI).

METHODS

Cardiomyopathy was induced in Sprague Dawley rats using high-dose isoproterenol. Nuclear [18F]FDG/PET and [99mTc]MIBI/SPECT were performed before and after isoproterenol administration. [18F]FDG (0.1 mCi, 200-400 µL) and [99mTc]MIBI (2 mCi, 200-600 µL) were administered via the tail vein and imaging was performed 1 hour postinjection. Isoproterenol-induced injury was confirmed by the plasma level of cardiac troponin and triphenyltetrazolium chloride (TTC) staining.

RESULTS

Isoproterenol administration resulted in an increase in circulating cardiac troponin I and showed histologic damage in the myocardium. Visually, preisoproterenol and postisoproterenol images showed alterations in cardiac accumulation of [18F]FDG, but not of [99mTc]MIBI. Image analysis revealed that myocardial uptake of [18F]FDG reduced by 60% after isoproterenol treatment, whereas that of [99mTc]MIBI decreased by 45%.

CONCLUSION

We conclude that [18F]FDG is a more sensitive radiotracer than [99mTc]MIBI for imaging of drug-induced cardiomyopathy. We theorize that isoproterenol-induced cardiomyopathy impacts cellular metabolism more than perfusion, which results in more substantial changes in [18F]FDG uptake than in [99mTc]MIBI accumulation in cardiac tissue.

Evaluation of skeletal muscle during calf exercise by 31-phosphorus magnetic resonance spectroscopy in patients on statin medications

Muscle pain is a common side effect of statin medications, but the cause is poorly understood. We characterized phosphocreatine (PCr) exercise recovery kinetics in 10 patients with hypercholesterolemia before and after a 4-week regimen of statin therapy using 31-phosphorus magnetic resonance spectroscopy ((31) P-MRS). (31) P spectra were obtained before, during, and after exercise on a calf flexion pedal ergometer. Creatine kinase (CK) serum levels were drawn before and after statin therapy. The mean metabolic recovery time constant in subjects increased from 28.1 s (SE = 6.5 s) to 55.4 s (SE = 7.4 s) after statin therapy. The unweighted mean of the pre/post-recovery time difference was -27.3 s (SE = 12.4 s; P = 0.02). Pre- and post-therapy CK levels were not significantly different (P = 0.50). Metabolic recovery time in the calf is prolonged in patients after statin use. This suggests that statins impair mitochondrial oxidative function, and (31) P MRS is a potential study model for statin-associated myopathy.

Decreased muscular radionuclide uptake in Tc-99m MIBI scintigraphy during paralytic phase of thyrotoxic periodic paralysis

The underlying pathophysiology of thyrotoxic periodic paralysis (TPP) is still obscure. From histologic surveys, vacuole formation and abundant mitochondrial abnormalities ranged from swelling, matrical pallor, pleomorphism, and reduced cristae were often disclosed in the muscle fibers during paralytic periods. In a 47-year-old man experiencing 2 episodes of transient paralysis, hyperthyroidism with TPP was diagnosed. During the acute paralytic phase, a significant reduction of radionucleotide uptake in the quadriceps on Tc-99m sestamibi scintigraphy was found, aside from the previous morphologic findings, that it further suggests impaired mitochondrial integrity and cellular viability in TPP.

A New Noninvasive Test to Detect Mitochondrial Dysfunction of Skeletal Muscles in Progressive Supranuclear Palsy

We present usage of technetium-99m methoxyisobutyl isonitrile (99mTc-sestamibi) single photon emission computed tomography (SPECT) as a novel noninvasive method to evaluate muscular mitochondrial function in patients with progressive supranuclear palsy (PSP). 99mTc-sestamibi SPECT revealed a statistically significant decrease in radionucleotide uptake in the quadriceps in PSP patients as compared with other neurodegenerative parkinsonism (P < 0.05) or control group (P < 0.05). This study demonstrates a remarkable deficit of skeletal muscle bioenergetics in patients with PSP. Our findings suggest a distinctive role of mitochondrial dysfunction in the pathogenesis of PSP. Furthermore, 99mTc-sestamibi SPECT provides a relatively simple, inexpensive, and noninvasive modality in further assessment of mitochondrial function and bioenergetic features in various muscular disorders.

New insights in the transcriptional activity and coregulator molecules in the arterial wall

A number of vascular diseases are associated with abnormal expression of genes that contribute to their pathophysiological and clinical manifestations, but at the same time offer potential therapeutic targets. One of the promising therapeutic approaches targets the pathophysiological pathways leading to aberrant gene activation, namely transcriptional activity and its molecular modulators (agonists, antagonists, coregulators, and nuclear receptors). The transcription factors can be divided into four classes (I-IV) classified by structural elements, like basic leucine zipper (bZIP) or basic helix-loop-helix (bHLH), which mediate their DNA binding activity but also determine the classes of drugs that can affect their activity. For example, statins modulate activation of the class-I transcription factor sterol responsive element-binding protein (SREBP), whose target genes including hydroxyl-methyl-glutaryl acetyl Coenzyme-A (HMG-CoA) reductase, HMG-CoA synthase, and the low-density lipoprotein receptor, all of which are involved in cholesterol and fatty acid metabolism. Similarly, insulin-like drugs target the nuclear receptor peroxisome-proliferator-activator-receptor (PPAR)-gamma (class-II), several anti-inflammatory drugs inhibit activation of nuclear factor kappa B (NFkappaB) (class-IV), while others (e.g. flavopiridol, rapamycin, and paclitaxel) target regulation of cell-cycle proteins. Increased understanding of the genetic and molecular basis of disease (e.g. transcriptional activity and its coregulation) will potentially enhance future diagnosis, treatment, and prevention of vascular diseases.

Muscular side effects of statins

Lipid lowering has been shown to be effective in preventing primary and recurrent cardiovascular events and to save life. Statins almost exclusively used for this purpose meanwhile became one of the most widely prescribed families of drugs world-wide. Myopathies--mainly not well characterized--are the major group of side effects. We here review different types of clinical appearances, localizations, symptoms and the biochemical background. The data indicate that severe muscular side effects are rare. Patients and their doctors, however, easily overlook mild ones. Myopathic symptoms without any known biochemical correlate are not rare. No general guideline exists about exact diagnosis and differential diagnosis. Strict adherence to the measures of life-style change and performance of regular exercise can even further enhance significantly these side effects. Much more research should be directed onto the pathophysiological (genetic?) background to finally evaluate possible therapeutic consequences rather than simply to withdraw or change the respective statin.