case 49

Presentation:

History: 62 year old female, with generalized pain.

What are the findings on planar whole body the bone scan?

Findings: Diffuse radiotracer uptake is noted in the cutaneous and subcutaneous tissues of the bilateral pelvic region and lower extremities. There is focal intense uptake in the lower thoracic spine corresponding to a compression fracture on recent CT. Additionally, moderate uptake is seen in the right first costochondral junction, which is also visible on the posterior view, correlating with chondral calcification on CT.

SPECT-CT demonstrates MDP uptake in widespread irregular calcifications within the subcutaneous fat and skin. These calcifications are a hallmark of calciphylaxis.

Question: What are the possible differential diagnoses of cutaneous/subcutaneus MDP uptake? 1.Calciphylaxis: Seen in patients with chronic kidney disease, this condition causes vascular calcification, resulting in subcutaneous radiotracer uptake. 2.Infection/inflammation: Cellulitis, dermatomyositis, polymyositis, abscess 3.Infarction: Acute muscle infarction, myonecrosis and calcification. 4.Metabolic: Hypercalcemia (renal failure, hyperparathyroidism), amyloidosis, hepatic failure 5.Traumatic: Heterotopic ossification (myositis ossificans),muscle necrosis, contusion, hematoma, electrical burns. 6.Vascular: Venous or lymphatic obstruction, lymphedema 7.Lymphedema: Lymphatic obstruction or dysfunction can cause diffuse soft tissue uptake due to fluid accumulation.

Discussion:

Calciphylaxis predominantly affects females and is most common in patients with end-stage renal disease, particularly those on hemodialysis.

The primary symptom is pain, with the lower extremities being the most frequently affected area.

Treatment often involves sodium thiosulfate. The prognosis is poor, with a high risk of septicemia due to compromised skin integrity; over 50% of patients die within a year of diagnosis.

References:

Wale, Daniel J., et al. "Extraosseous findings on bone scintigraphy using fusion SPECT/CT and correlative imaging." American Journal of Roentgenology 205.1 (2015): 160-172.
Gnanasegaran, Gopinath, et al. "Patterns, variants, artifacts, and pitfalls in conventional radionuclide bone imaging and SPECT/CT." Seminars in nuclear medicine. Vol. 39. No. 6. WB Saunders, 2009.

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