Molecular imaging in MSK radiology: Where are we going?

Musculoskeletal (MSK) pathologies are one of the leading causes of disability worldwide. However, treatment options and understanding of pathogenetic processes are still partially unclear, mainly due to a limited ability in early disease detection and response to therapy assessment. In this scenario, thanks to a strong technological advancement, structural imaging is currently established as the gold-standard of diagnosis in many MSK disorders but each single diagnostic modality (plain films, high-resolution ultrasound, computed tomography and magnetic resonance) still suffer by a low specificity regarding the characterization of inflammatory processes, the quantification of inflammatory activity levels, and the degree of response to therapy. To overcome these limitations, molecular imaging techniques may play a promising role. Starting from the strengths and weaknesses of structural anatomical imaging, the present narrative review aims to highlight the promising role of molecular imaging in the assessment of non-neoplastic MSK diseases with a special focus on its role to monitor treatment response.

Pathogenesis, Diagnosis and Management of Polymyalgia Rheumatica

Polymyalgia rheumatica is an inflammatory rheumatic disease of the elderly characterised by pain and stiffness in the neck and pelvic girdle, and is the second most common inflammatory rheumatic condition in this age group, after rheumatoid arthritis. Polymyalgia rheumatica can occur independently or in association with giant cell arteritis, which is the most common form of primary vasculitis. The diagnosis of polymyalgia rheumatica is usually based on clinical presentation and increase of inflammatory markers. There are no pathognomonic findings that can confirm the diagnosis. However, different imaging techniques, especially ultrasonography, can assist in the identification of polymyalgia rheumatica. Glucocorticoids are the cornerstone of the treatment of polymyalgia rheumatica, but they might be associated with different adverse events. A subgroup of patients presents with a refractory disease course and, in these cases, adding methotrexate as a steroid-sparing agent could be useful. In this review, we summarise the latest findings regarding the pathogenesis, diagnosis and management of polymyalgia rheumatica and try to highlight the possible pitfalls, especially in elderly patients.

Interspinous bursitis is common in polymyalgia rheumatica, but is not associated with spinal pain

Introduction

Polymyalgia rheumatica (PMR) is a common inflammatory disease in older people characterized by shoulder and/or pelvic girdle, and cervical and, occasionally, lumbar pain. Interspinous bursitis has been suggested as a potential cause of spinal symptoms. We evaluated, by 18 F-fluorodeoxyglucose (FDG) positron emission tomography integrated with computed tomography (PET/CT), the vertebral structures involved in PMR in a cohort of consecutive, untreated patients.

Methods

Sixty-five consecutive patients with PMR were studied. After a standardized physical examination, which included evaluation of pain and tenderness in the vertebral column, they underwent FDG-PET/CT. Sites of increased uptake and their correlation with spontaneous and provoked pain were recorded. For comparison, FDG-PET/CT was performed also in 65 age- and sex-matched controls and in 10 rheumatoid arthritis (RA) patients.

Results

The most frequent site of spontaneous and provoked pain was the cervical portion. FDG uptake was more frequent in the lumbar portion than at any other location, and in the cervical rather than in the thoracic portion (P <0.0001). No correlation was found between uptake and spontaneous or provoked pain. There was an association between presence of cervical and lumbar bursitis (r = 0.34, P = 0.007). None of the control patients and one out of ten RA patients showed interspinous bursitis.

Conclusions

Interspinous bursitis is a frequent finding in the lumbar spine of patients with PMR. However, it is not associated with clinical symptoms and can hardly explain the spinal pain reported by the patients. Cervical pain is more frequent than lumbar pain in PMR patients and may be caused by shoulder girdle involvement.

High frequency of capsular knee involvement in polymyalgia rheumatica/giant cell arteritis patients studied by positron emission tomography

OBJECTIVE

Peripheral arthritis has been described in up to 50% of PMR patients, with knee involvement in the majority. This study was designed to evaluate by PET/CT the knees of patients with PMR and GCA and to identify the knee structures involved by inflammation.

METHODS

Twenty-five consecutive patients with PMR (19) or GCA (6) were studied in comparison with 25 age- and sex-matched controls who underwent PET/CT for initial staging of cancer. Clinical features, ESR and CRP were evaluated. Simultaneous FDG-PET and CT imaging from the skull base to the knee was performed after injection of 4.8-5.2 MBq of [(18)F]FDG per kilogram body weight. The knee anatomical structures being evaluated included joints, fibrous capsule, synovial recesses and bursae.

RESULTS

At PET/CT, 21/25 patients (84%) showed bilateral diffuse uptake at the knees. The tracer clearly outlined the contour of the fibrous capsule. In 50 knees, 90% of capsular sites were involved by inflammation in comparison with 23% of intracapsular sites and 4.7% of extracapsular sites (P < 0.0001). No correlation was found between PET/CT results and ESR or CRP. FDG uptake, with a pattern similar to that observed in 96% of PMR/GCA patients, was seen in 20% of controls (P = 0.03).

CONCLUSION

Our findings suggest that bilateral capsulitis of the knee is detectable in most PMR/GCA patients if a sensitive imaging technique such as PET/CT is used.

Imaging of polymyalgia rheumatica: indications on its pathogenesis, diagnosis and prognosis

OBJECTIVES

Imaging is one of the most appealing techniques to explore PMR, a disease whose causes, development mechanisms and anatomical targets of inflammatory damage are still scarcely known. This review is concerned with an appraisal of PMR with different imaging modalities with a view to highlighting possible clues to its pathogenesis, diagnosis and prognosis.

METHODS

A systematic literature research was performed searching PubMed until July 2010. The Cochrane Library was searched for the relevant reviews, and the abstracts of the ACR and European League Against Rheumatism congresses of the period 2005-10 were reviewed.

RESULTS

A total of 1059 papers were retrieved, 46 of which were selected at the end of the review process; 6 of them were concerned with two different imaging techniques. Of these papers, 6 (11.5%) were concerned with conventional radiology; 8 (15.4%) with scintigraphy; 17 (32.7%) with ultrasonography (US); 15 (28.8%) with MRI; and 6 (11.5%) with PET. MRI, US and PET appeared to be the most promising imaging techniques. Bilateral subacromial bursitis, biceps long head tenosynovitis and trochanteric bursitis were particularly consistent findings. In addition, MRI and PET showed interspinous bursitis and PET frequently showed large-vessel vasculitis. Few papers have addressed the role of imaging for diagnosis, differential diagnosis and prognosis of PMR.

CONCLUSIONS

Imaging plays an important role in the comprehensive evaluation of PMR, including its pathogenesis, diagnosis and prognosis. Most of its potential is still unexplored, which fact should stimulate further research.

Increased muscle interstitial levels of inflammatory cytokines in polymyalgia rheumatica

OBJECTIVE

Polymyalgia rheumatica (PMR) is characterized by aching of the proximal muscles and increased blood levels of markers of inflammation. Despite the muscle complaints, the current view is that symptoms are caused by inflammation in synovial structures. The purpose of this study was to elucidate the disease mechanisms in symptomatic muscles by measuring interstitial levels of cytokines before and after prednisolone treatment.

METHODS

Twenty glucocorticoid-naive patients newly diagnosed as having PMR and 20 control subjects were studied before and after 14 days of prednisolone therapy (20 mg/day). Interstitial concentrations of interleukin-1α/β (IL-1α/β), IL-1 receptor antagonist, IL-6, IL-8, tumor necrosis factor α (TNFα), and monocyte chemoattractant protein 1 were measured in symptomatic vastus lateralis and trapezius muscles using the microdialysis technique. Plasma levels were measured simultaneously.

RESULTS

Prednisolone abolished symptoms in all of the PMR patients within 1-2 days; the erythrocyte sedimentation rate and C-reactive protein levels were normalized on day 14. In both muscles, interstitial concentrations of all cytokines were markedly higher (P < 0.05) in the PMR patients than in the controls before treatment. In both patients and controls, interstitial levels of most cytokines were higher than plasma levels, with the exception of IL-1α and TNFα, which were lower in both groups. In the PMR patients, interstitial concentrations were normalized after prednisolone treatment.

CONCLUSION

This study introduces a novel view of PMR, indicating that increased interstitial levels of inflammatory cytokines in symptomatic muscles play a role in the pathophysiology of the disease and that cytokines may be released locally. To explore the disease specificity, similar studies in other primary inflammatory conditions are warranted.

Elevated muscle interstitial levels of pain-inducing substances in symptomatic muscles in patients with polymyalgia rheumatica

Polymyalgia rheumatica (PMR) is characterized by aching proximal muscles and systemic inflammation. We explored the pain-eliciting mechanisms by measuring interstitial levels in muscle of potentially pain-inducing substances as well as local blood flow. Twenty glucocorticoid-naive patients with newly diagnosed PMR and 20 controls were examined before and after 14 days of prednisolone (20 mg/day). Concentrations of glutamate, prostaglandin E(2) (PGE(2)), bradykinin, serotonin, adenosine triphosphate, lactate, pyruvate, and potassium as well as extraction of (3)H(2)O were measured in symptomatic vastus lateralis and trapezius muscles using microdialysis. Plasma levels were measured simultaneously. To be considered potentially pain inducing, interstitial concentrations of candidates should be higher in patients vs. controls, be normalized by prednisolone, and be higher in muscle vs. plasma. Prednisolone abolished symptoms in all patients within 2 days. Before treatment glutamate in both muscles (vastus: 60±7 vs. 38±7 μmol/L; trapezius: 60±6 vs. 43±7 μmol/L) and PGE(2) in vastus (911±200 vs. 496±122 pg/mL) were higher in patients than in controls (P<0.05), and higher in muscle than in plasma (P<0.05). Prednisolone abolished the differences between patients and controls. No other candidate completely fulfilled the predefined requirements for pain-inducing substances in PMR. (3)H(2)O extraction was identical between groups. In conclusion, local release of glutamate and PGE(2), but not ischemia, may contribute to the muscle pain in PMR. This supports the view that intramuscular mechanisms are important in PMR.

Polymyalgia rheumatica is associated with extensor tendon tenosynovitis but not with synovitis of the hands: a magnetic resonance imaging study

OBJECTIVES

To study with MRI the hands of consecutive PMR patients, who were not selected on the basis of peripheral arthritis, with a correlation to clinical and laboratory findings.

METHODS

Twenty-six hands of 15 PMR patients and 26 hands of 13 healthy controls were studied by extremity-dedicated MRI for the presence of synovitis, tenosynovitis, soft-tissue oedema, bone marrow oedema and erosions.

RESULTS

Sixteen (61.6%) of the 26 PMR hands and 4 (15.4%) of the 26 control hands showed tenosynovitis (P = 0.001). Extensor tendon tenosynovitis was seen in 9 (34.6%) of the 26 PMR hands, but in only 1 (3.8%) control hand (P = 0.002) and flexor tenosynovitis was seen in 12 (46.1%) of the 26 PMR hands and in 4 (15.4%) of the 26 control hands (P = 0.03). All other features were similar in the two groups.

CONCLUSIONS

Our data support the view that tenosynovitis, especially of the extensor tendons, is a frequent event in PMR, unrelated to clinical involvement of the hand. This finding is in agreement with the concept of PMR as a disease of extra-articular structures.