Background: The most frequent complications of joint arthroplasty are septic or aseptic loosening of endoprostheses. Preoperative differentiation is essential, since very different treatment methods result from the diagnoses. The aim of the current study was to evaluate the clinical value of ¹⁸F-Fluoro-deoxyglucose positron emission tomography (¹⁸F-FDG PET) as a diagnostic modality for inflammation and loosening in hip and knee joint prostheses. Methods: ¹⁸F-FDG-PET examinations and multiphase bone scan were performed on hip and knee endoprostheses in 27 patients prior to revision surgical procedures planned for prosthetic loosening. Intact prostheses were found at the opposite site in some patients so that additional 9 joints could be examined with the field of view of ¹⁸F-FDG PET. Verification and valuation of the PET and scintigraphic image findings were conducted by comparing them with information combined from intraoperative findings, histopathology, and microbiological investigations. Results: Evidence of loosening was correctly determined in 76.4% of cases using ¹⁸F-FDG-PET, and in 75% of cases using bone scan. The detection of periprosthetic inflammation using ¹⁸F-FDG-PET had a sensitivity of 100% for septic cases and of 45.5% in cases of increased abrasion and aseptic foreign-body reactions. However, reliable differentiation between abrasion-induced and bacterial-caused inflammation was not possible using ¹⁸F-FDG-PET. Conclusion: ¹⁸F-Fluoro-deoxyglucose positron emission tomography (¹⁸F-FDG-PET) allows reliable prediction of peri-prosthetic septical inflammatory tissue reactions. Because of the high sensitivity of this method, a negative PET result in the setting of a diagnostically unclear situation eliminates the need for revision surgery. In contrast, a positive PET result gives no clear differentiation regarding the cause of inflammation.

Background: A number of studies show that the serum levels of antithyroid peroxidase antibodies (TPO-Ab) in patients with Hashimoto's thyroiditis decline during levothyroxine treatment, but do not provide quantitative data or report the fraction of patients in whom test for TPO-Ab became negative (“normalization percentage”). The objective of the present study was to provide this information. Methods: This was a retrospective study of TPO-Ab concentrations in 36 women and 2 men (mean age 51 ± 16 years; range 19–81 years) with Hashimoto's thyroiditis as defined by the following criteria: elevated plasma TPO-Ab and typical hypoechogenicity of the thyroid in high-resolution sonography at first presentation or during follow-up and low pertechnetate uptake in thyroid scintigraphy. When first studied 17 women and 1 man were not yet taking levothyroxine. The remaining 20 patients were receiving levothyroxine. At initial examination 18 patients had serum thyroid-stimulating hormone (TSH) concentrations above normal. Results of up to eight (mean = 5.8) measurements obtained over a mean period of 50 months while patients were receiving levothyroxine were analyzed. In addition, serum TSH, free triiodothyronine (fT3), and free thyroxine (fT4) were measured, and ultrasound of the neck was performed at each follow-up examination. Results: In terms of TPO-Ab levels, 35 of 38 patients (92%) had a decrease, 2 patients had undulating levels, and 1 patient had an inverse hyperbolic increase in her TPO-Ab levels. In the 35 patients in whom there were decreasing TPO-Ab values, the mean of the first value was 4779 IU/mL with an SD of 4099 IU/mL. The mean decrease after 3 months was 8%, and after 1 year it was 45%. Five years after the first value, TPO-Ab levels were 1456 ± 1219 IU/mL, a decrease of 70%. TPO-Ab levels became negative, < 100 IU/mL, in only six patients, a normalization percentage of 16%. There were no correlations between changes in thyroid volume and changes in TPO-Ab. Conclusion: Serum TPO-Ab levels decline in most patients with Hashimoto's thyroiditis who are taking levothyroxine, but after a mean of 50 months, TPO-Ab became negative in only a minority of patients.

Background: Structural follow-up magnetic resonance imaging (MRI) after stereotactic radiosurgery (SRS) for brain metastases frequently displays local changes in the area of applied irradiation, which are often difficult to interpret (e.g., local tumor recurrence, radiation-induced changes). The use of stereotactic biopsy for histological assessment of these changes has a high diagnostic accuracy and can be considered as method of choice. In order to solve this relevant clinical problem non-invasively, advanced MRI techniques and amino acid positron-emission-tomography (PET) are increasingly used. Case presentation: We report the long-term follow-up of a patient who had been treated with linear accelerator based SRS for cerebral metastases of a lung cancer. Fifty-eight months after SRS, the differentiation of local recurrent brain metastasis from radiation-induced changes using structural MRI was difficult. For further differentiation, perfusion-weighted MRI (PWI), proton magnetic resonance spectroscopy (MRS), and ¹¹C-methyl-L-methionine (MET) PET was performed. Due to artifacts and technical limitations, PWI MRI and MRS findings were not conclusive. In contrast, MET PET findings were suggestive for radiation-induced changes. Finally, a stereotactic biopsy for histological assessment of these changes demonstrated clearly a radiation-induced necrosis and the absence of vital tumor. Conclusion: The use of stereotactic biopsy for histological assessment of indistinguishable lesions on structural MRI after SRS for treatment of brain metastasis represents a highly reliable method to differentiate local tumor recurrence from radiation-induced changes. In this field, results of studies with both advanced MRI techniques and amino acid PET suggest encouraging results. However, artifacts and technical limitations (e.g., lesion size) are still a problem and comparative studies are needed to investigate the relationship, diagnostic performance, and complementary character of advanced MRI techniques and amino acid PET.

Background Infections of the spine are rare and often discovered late, but they can have a severe outcome with hospital case fatality rates of up to 17%. Efficient and early diagnosis is important, because early diagnosis and therapy improve outcome. The aim of the current study was to evaluate the clinical value of ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) uptake pattern in PET as a diagnostic modality for the detection of spondylodiscitis. Materials and methods ¹⁸F-FDG-PET examinations of the spine were performed in 42 patients with suspected spondylodiscitis. Of these 42 patients, 13 had already undergone spinal surgery in the past, making initial definition of the test group difficult and complex. Qualitative analysis was based on ¹⁸F-FDG uptake patterns, and quantitative maximal standard uptake value measurements were ascertained. PET findings were verified by comparing them with combined information from intraoperative findings, blood results, microbiological investigations, histopathology, and clinical examination. Results Evidence of spondylodiscitis was correctly determined in 95% of patients and absence of spondylodiscitis in 86% of patients using ¹⁸F-FDG-PET. The detection of spondylodiscitis by ¹⁸F-FDG-PET had a sensitivity of 86% and a specificity of 95%. Three patients had false-negative and one patient a false-positive finding on ¹⁸F-FDG-PET. Conclusion The application of ¹⁸F-FDG uptake patterns in ¹⁸F-FDG-PET helps to predict or exclude spondylodiscitis. Differentiation between inflammatory and degenerative changes in the vertebral body endplates is possible. Owing to the high specificity of this method, a negative PET result in the setting of a diagnostically unclear case diminishes the need for surgical intervention. ¹⁸F-FDG-PET is therefore an important tool in inflammation imaging and can be used in the diagnostic cascade of difficult cases with suspected spondylodiscitis. In contrast, a positive PET result does not always clearly establish the cause of increased ¹⁸F-FDG uptake.