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Objective:
Amyloidosis is a rare disease process that can affect a wide range of the body’s organ systems. It results from insoluble misfolded proteins depositing into the extracellular space and may manifest differently depending on the location and protein subtype involved. Musculoskeletal amyloidosis (MA) serves a diagnostic challenge due to its vague and nonspecific symptoms: fatigue, bone pain, and weakness. If diagnosis of MA is delayed without treatment it may result in up to a 50% mortality rate within 2 years for patients. However, many effective treatment options are available for most subtypes dependent on levels of deposition if an early diagnosis is made. This presentation will review a multimodal case series of five patients diagnosed with amyloidosis presenting with rare and unusual musculoskeletal manifestations.

Materials and Methods:
Medical imaging for five patients, all men with ages from 61 - 65 years, was acquired during diagnostic workup of patients with vague musculoskeletal symptoms. The anatomical regions affected include the hip, knee, wrist, femur, and abdominal wall. The imaging modalities utilized in this case series include computed tomography (CT) (four patients), selected MR sequences to includeT1/T2/STIR (four patients), ultrasound (two patients), plain film (two patients), and positron emission technology PET/CT (one patient). All five patients were eventually diagnosed with pathologically-proven amyloidosis.

Results:
The most commonly affected joints in MA include the elbows, wrists, shoulders, and pelvis. Plain films may show osseous erosion, lytic lesions with well-defined borders, and occasionally pathologic fractures. CT shows similar findings as plain films often to greater advantage, including fine calcification and the “shoulder pad" sign of prominent anterior soft tissues due to periarticular and/or deltoid muscle deposition of amyloid. MRI can often evaluate the nerve and soft tissue manifestations of MA to include the shoulder pad sign, demonstrate the tenosynovial giant cell tumor mimic (formerly pigmented villonodular synovitis), including a moderately contrast-enhancing lesion with T1 and T2-hypointense signal, and support the diagnosis of carpal tunnel syndrome, including loss of T2 signal in the median nerve. Ultrasound may demonstrate calcification, joint effusions, or deposition of soft tissue proteins and is a useful screening tool. Lastly, fluorodeoxyglucose (FDG) PET may aid in the surveillance of plaque deposition, given the avidity of myofibrillar plaques on imaging.

Conclusion:
Rapid tissue sampling and treatment of MA directly impact patient morbidity and mortality. Due to its rarity and nonspecific symptoms, an interprofessional approach including radiologists is essential in improving outcomes. Our case series thus outlines radiographic findings across multiple modalities in patients with biopsy-proven MA to help reduce the diagnostic uncertainty of the disease, aid in expedited tissue sampling, and allow for radiographic trending of treatment response in a hope to improve patient overall outcomes, and quality of life.