The Metabolic Superscan

Introduction: Superscan on Bone scintigraphy is characterized by diffusely increased tracer uptake throughout the skeleton accompanied by decreased renal visualization. Superscan is often seen in metastatic setting to the bones, notably in Carcinoma Prostate. However, it may also occur in metabolic bone diseases such as Hyperparathyroidism, Paget disease, Osteomalacia, and myelofibrosis. This exhibit focuses on patterns of superscan that may be obtained in various metabolic diseases.

Methods: Superscan can arise in metabolic conditions that result in alteration of skeletal remodelling due to high turnover. They are so-called as the scan quality appears apparently good which is in fact due to diffusely increased skeletal uptake. The increased skeletal tracer uptake is due to increased osseous clearance and not the reduced renal clearance of MDP. A metabolic superscan is unrelated to the marrow distribution and can usually be differentiated from that of malignancy due to presence of irregularity of uptake and focal abnormalities in the latter that is often appreciated in the ribs or ends of long bones. Hence, in a metabolic superscan tracer uptake is more uniform and closely mimics the normal distribution of tracer.

Results: Hyperparathyroidism (primary, secondary, or tertiary) is the most frequent cause of metabolic superscan. Superscan can also arise in renal osteodystrophy, distal renal tubular acidosis, hyperthyroidism, Fanconi syndrome, acromegaly, fluorosis, and hypervitaminosis A.

Conclusions: Understanding patterns of superscans in metabolic diseases and metastatic settings is important, and may help in accurate interpretation for obtaining maximum yield out of the bone scintigraphy studies.