[Imaging in monoclonal plasma cell disorders : Multiple myeloma, smouldering multiple myeloma and MGUS]

Imaging has a key diagnostic role in monoclonal plasma cell disorders. It can be used not only to detect osteolytic skeletal lesions but also for the detection of bone marrow involvement, extramedullary manifestations, impending complications, treatment response and the relapse assessment. Whole-body computed tomography (CT) has replaced the conventional skeletal survey, while whole-body magnetic resonance imaging (MRI) and ¹⁸F-fluorodeoxyglucose positron emission tomography-CT (FDG PET/CT) supplement the morphological skeletal assessment by depicting the bone marrow and functional-metabolic disease activity.

This article provides a practical, guideline-based overview of imaging in monoclonal gammopathy of undetermined significance (MGUS), smouldering multiple myeloma (SMM) and active (requiring treatment) multiple myeloma (MM), focusing on the indications, technical implementation, interpretation of results, structured reporting and clinical consequences.

Narrative synthesis of relevant publications and guidelines, including literature available through June 2026.

In cases of active MM, whole-body CT is recommended at the time of making the diagnosis to assess skeletal damage. Whole-body MRI or 18F-FDG PET/CT can be additionally used to evaluate bone marrow involvement, metabolic activity and paraskeletal or extramedullary disease manifestations. In selected non-IgM MGUS with a high risk of progression according to the German S3 algorithm and in SMM, whole-body CT is primarily used to differentiate from MM. If osteolysis is not detected, whole-body MRI or alternatively 18F-FDG PET/CT is performed. More than one focal MRI lesion typical for myeloma each measuring ≥ 5 mm is a myeloma-defining event. Follow-up and response to treatment should preferentially use the modality that best depicted the baseline disease. In serologically measurable disease, follow-up is predominantly clinical and laboratory-based. Imaging follow-up is required in hyposecretory or nonsecretory MM, in patients with new clinical symptoms, or in the presence of soft-tissue involvement.

Radiological imaging reports of plasma cell disorders should be standardized in a way specific for the modality and directed at the clinical issue. Decisive is the distinction between mineralized bone and bone marrow, the assessment of instability risk, the separate description of paraskeletal and true extramedullary manifestations as well as the transparent classification of the response, stable findings or progression. A structured whole-body reporting facilitates interdisciplinary treatment planning in the myeloma board.