Radiologic Manifestations of Musculoskeletal Sarcoidosis

Myositis and Its Mimics: Guideline Updates, MRI Characteristics, and New Horizons

Myositis is defined as inflammation within skeletal muscle and is a subcategory of myopathy, which is more broadly defined as any disorder affecting skeletal muscle. Myositis may be encountered as a component of autoimmune and connective tissue disease, where it is described as idiopathic inflammatory myopathy. Myositis can also be caused by infections, as well as toxins and drugs, including newer classes of medications. MRI plays an important role in the diagnosis and evaluation of patients with suspected myositis, but many entities may have imaging features similar to myositis and can be considered myositis mimics. These include muscular dystrophies, denervation, deep venous thrombosis, diabetic myonecrosis, muscle injury, heterotopic ossification, and even neoplasms. In patients with suspected myositis, definitive diagnosis may require integrated analysis of imaging findings with clinical, laboratory, and pathology data. The objectives of this article are to review the fundamental features of myositis, including recent updates in terminology and consensus guidelines for idiopathic inflammatory myopathies, the most important MRI differential diagnostic considerations for myositis (i.e., myositis mimics), and new horizons, including the potential importance of artificial intelligence and multimodal integrated diagnostics in the evaluation of patients with muscle disorders.

Imaging Features of Pediatric Sarcoidosis

Sarcoidosis is a granulomatous inflammatory disease of uncertain cause. It occurs most commonly in young and middle-aged adults and less frequently in children; therefore, few data on pediatric sarcoidosis exist in the literature. The diagnosis and management of sarcoidosis remain challenging because of diverse and often nonspecific clinical and imaging findings. In addition, the clinical picture varies widely by age. Prepubertal and adolescent patients often present with adult-like pulmonary disease; however, early-onset sarcoidosis is typically characterized by the triad of arthritis, uveitis, and skin rash. Sarcoidosis is mostly a diagnosis of exclusion made by demonstrating noncaseating granulomas at histopathologic examination in patients with compatible clinical and radiologic findings. Although sarcoidosis often affects the lungs and thoracic lymph nodes, it can involve almost any organ in the body. The most common radiologic manifestation is pulmonary involvement, characterized by mediastinal and bilateral symmetric hilar lymphadenopathies with perilymphatic micronodules. Abdominal involvement is also common in children and often manifests as hepatomegaly, splenomegaly, and abdominal lymph node enlargement. Although neurosarcoidosis and cardiac sarcoidosis are rare, imaging is essential to the diagnosis of central nervous system and cardiac involvement because of the risky biopsy procedure and its low diagnostic yield due to focal involvement. Being familiar with the spectrum of imaging findings of sarcoidosis may aid in appropriate diagnosis and management. ©RSNA, 2023 Test Your Knowledge questions are available in the supplemental material.

Sarcoid dactylitis: A case report of rare presentation of uncommon disease, sarcoidosis-From Ethiopia

We present a rare case of sarcoid dactylitis after an adult female presented with painless swelling of the bilateral hand fingers and toe, with radiographic findings highly characteristic for osseous sarcoidosis and confirmation made by bronchoscopic biopsy of hilar enlarged lymph nodes.

Granulomatous myopathy: Sarcoidosis and beyond

Non-necrotizing granulomatous inflammation is a rare but easily recognized histopathological finding in skeletal muscle biopsy. A limited number of diseases are known to be associated with non-necrotizing granulomatous myopathy. Once identified, a careful evaluation for evidence of extramuscular granulomatosis and other signs suggestive of sarcoidosis is warranted as about half of the patients have sarcoid myopathy. In addition, the presence of granulomatous myopathy should trigger a search for clinical and pathological clues of inclusion body myositis (IBM), which accounts for most of the remaining patients and can coexist with sarcoidosis. Recognizing the features of IBM in patients with granulomatous myopathy can potentially spare the patients from unnecessary exposure to immunosuppressive therapies. In patients whose granulomatous myopathy remain unexplained, further investigations should aim at identifying myasthenia gravis and other autoimmune disorders, especially those known to cause granulomatous inflammation in other organs. Laboratory investigations should include acetylcholine receptor, antimitochondrial, antineutrophil cytoplasmic, thyroglobulin, and thyroid peroxidase autoantibodies. In the appropriate clinical context, exposure to immune checkpoint inhibitors and chronic graft-vs-host disease can be causes of granulomatous myopathy. In cases of unexplained granulomatous myopathy, natural killer/T-cell lymphoma should be considered and careful histopathological examination for atypical cells and appropriate immunostaining is crucial. Identifying the etiology of granulomatous myopathy in each patient can guide appropriate treatment.

Clinical characteristics and outcome in muscular sarcoidosis: a retrospective cohort study and literature review

We evaluated the clinical features and treatment response of patients with muscular sarcoidosis. A retrospective cohort of 12 patients showed muscle weakness in 11 and myalgia in seven. One had focal myositis. Four had a negative medical history for sarcoidosis. Muscle imaging showed muscle edema in all and replacement of muscle tissue by fat in half of patients. Muscle biopsy showed non-caseating granulomas in six of nine patients and inflammation without granulomas in three. None of the muscle biopsies showed features of inclusion body myositis. Imaging in three patients without muscle biopsy showed focal intramuscular masses or a 'tiger man' appearance typical for muscular sarcoidosis. Treatment consisted of glucocorticoids in 11, additional methotrexate or azathioprine in seven and infliximab in two patients. Half of the patients had symptoms leading to substantial disability (modified Rankin scale score >1) at last follow-up. A literature review of articles describing more than one muscular sarcoidosis patient published in the last 25 years identified 153 additional patients. We found muscular sarcoidosis to be a rare and often disabling disease which may be recognized by typical muscle imaging characteristics and add focal myositis to the muscular phenotypes of sarcoidosis.

Muscular sarcoidosis in the eyes of 18 F-FDG PET/CT

PURPOSE

The aim of this study was to determine the frequency, symptoms, activity and pattern of muscle sarcoidosis, correlation with laboratory parameters, and to assess its therapy response with ¹⁸ F-FDG PET/CT.

METHODS

Study included 90 patients with biopsy confirmed sarcoidosis and symptoms/biochemical/imaging findings suggestive of active disease. The exclusion criteria were: presence of cancer or other diseases that resemble sarcoidosis on PET/CT (Wegener syndrome, tuberculosis, aspergillosis), and the glucose level being greater than 11 mmol/L. All patients were screened for muscle sarcoidosis with ¹⁸ F-FDG PET/CT examination. Follow-up examination was done 1 year after the baseline in order to evaluate therapy response.

RESULTS

Disease was very rare and present in only 7/90 patients. Most of the patients had polysymptomatic disease, while muscle pain was less frequent, present only in one-third of the patients. The disease was usually present in the lower limbs, upper limbs, and skeletal striated muscles. The most common pattern of disease was nodular. Disease activity estimated with SUVmax was not in correlation with the ACE findings, creatine kinase, and aldolase levels (p > 0.05). Follow-up PET/CT revealed complete remission in one patient and partial remission in two.

CONCLUSION

¹⁸ F-FDG PET/CT can be useful in asymptomatic young patients with nodular pattern of disease, who have easily relapsing form of disease. It can help in further management of these patients and can affect prognosis of the disease, since most of the laboratory parameters in this entity are within normal limits.

Musculoskeletal Manifestations of Sarcoidosis

Since its initial description in the late 19th century, sarcoidosis has been extensively studied. Although the general mechanism of immune activation is known, many details especially in the context of disease associations are still missing. One of such associations is the musculoskeletal complications that are widely variable in terms of presentation and response to treatment. Sarcoidosis can involve the joints leading to acute and, less commonly chronic, arthritis. While acute arthritis is mostly self-resolving in nature, chronic arthritis may lead to deformity and destruction of the joint. Sarcoidosis can also involve the muscles, leading to different pathologies primarily categorized according to the clinical presentation, despite the efforts to find a new classification based on imaging, histological, and clinical findings. The bones can be directly and indirectly affected. Different types of bone lesions have been described, although around half of these patients remain asymptomatic. Osteoporosis, increased risk of fractures, hypercalcemia, and hypercalciuria are examples of the indirect effect of sarcoidosis on the bones, possibly contributed to elevated levels of calcitriol. Nevertheless, sarcoidosis can be associated with small-vessel, medium-vessel, and large vessel vasculitis, although it is frequently difficult to differentiate between the co-existence of a pure vasculitis and sarcoidosis and sarcoid vasculitis.

Bilateral swelling of the forearms revealing muscular sarcoidosis: a case-based review

Muscular sarcoidosis is rarely symptomatic and mainly affects proximal muscles of the lower extremities. However, the distal localization in the upper extremities is rare. We used systematic approach to analyze all relevant literature review and we identified only three cases of muscular sarcoidosis of the upper extremities. We report the case of a 56-year-old woman who presented distal and bilateral swelling of the extensor surface of the forearms revealing muscular sarcoidosis. The laboratory exams associated elevated acute phase reactants with elevated serum angiotensin-converting enzyme levels and normal serum muscle enzymes. Ultrasound and MRI showed a bilateral and symmetrical muscle hypertrophy of the extensors of the fingers. Histological examination of muscle specimen and minor salivary gland biopsy revealed noncaseating epithelioid-cell granulomas. Therefore, the diagnosis of muscular sarcoidosis of the finger extensor muscles was made. Swelling of the forearms disappeared gradually under prednisolone 1 mg/kg/day. We used methotrexate as a steroid-sparing agent. Muscular MRI in sarcoidosis is not specific, but is to make a diagnosis of the lesion to optimize the biopsy which the cornerstone of the diagnosis ofsarcoidosis.