Joint Program in Nuclear Medicine

Imaging of Acute Osteomyelitis in the Diabetic Foot

Pritinder K. Thind, MD
Donald E. Tow, MD
David E. Drum, MD PhD

September 21, 1999

Presentation

A 65 year old male with a history of non-insulin dependent diabetes mellitus, alcohol abuse, and severe peripheral vascular disease presented with a non-healing ulcer of the left first toe.

Imaging Technique

Three Phase Bone Scan

25 millicuries of Tc-99m MDP were administered intravenously. Dynamic 2-5 second images were obtained for 60 seconds after injection (angiographic phase). A static tissue phase image was obtained. Delayed skeletal phase images were obtained at 2-4 hours after injection.

Gallium Scan

5 millicuries of Ga- 67 citrate were administered intravenously. Delayed images of the feet were obtained at 48 hours.

Imaging Findings

Radiography, three phase bone scan and gallium scan were performed.

Radiograph

The radiograph shows osteopenia of the first digit, soft tissue swelling and bone resorption of the first toe.

Three Phase Bone Scan

The flow phase of the three-phase bone scan demonstrates diffuse increased flow to the left foot with focal accumulation in the first digit (the arrow shows the accumulation). On the tissue phase, there is marked asymmetry with increase activity in the left foot. In addition, there is mild localization in the first digit (shown by arrow). The delayed images demonstrate focal uptake at the left first MTP joint and first interphalangeal joint (shown by arrows).

Gallium Scan

The gallium scan (bottom two images) demonstrates focal increased tracer uptake in the left first toe (shown by arrow). The intensity of the gallium uptake on the bottom two images is greater than that of the delayed bone scan on the top two images.

Discussion

Diabetes mellitus affects 5% of the U.S. population. Twenty percent of adult hospitalized diabetic patients have foot disorders leading to significant disability (1). One third of patients have evidence of osteomyelitis. Contributing factors include angiopathy and peripheral neuropathy.

Imaging techniques for osteomyelitis include:

Radiography

Radiographs can vary in appearance. They can be normal or demonstrate soft tissue swelling, periosteal reaction, subperiosteal bone resorption, and erosions and sequestra. Radiographs are the least sensitive method of diagnosis. Lipman at al reported a sensitivity of 67%, specificity of 40% and accuracy of 50% (2).

Three Phase Bone Scintigraphy

The uptake in three phase bone scans is related to blood flow and osteoblastic activity. In the study by R.H. Gold et al, the mean sensitivity is 85% and the specificity is 54% (3).

Gallium Scintigraphy

Mechanisms of Ga-67 citrate uptake include: Criteria for a positive gallium scan include uptake: In Johnson et al, 22 patients were evaluated. The results yielded a sensitivity of 100%, specificity of 40% and accuracy of 73% (4). In Schauwecker’s review of the literature, the sensitivity was 81% with a specificity of 69% (5). Gallium has a proven role in the monitoring of treatment.

Indium-111 labeled leukocyte scintigraphy

Indium-111 labeled leukocytes localize in infectious and inflammatory lesions by leukotaxis. Images are obtained at 2 to 4 hours as well as 24 hours. Drawbacks include the low count rate, cost of the radiopharmaceutical preparation, complexity of the labeling and lack of bony landmarks. Johnson et al showed a sensitivity of 100%, specificity of 70% and accuracy of 86%. When combined with bone scan, the specificity increased to 80% and the accuracy increased to 91% (4).

MRI

On MRI, osteomyelitis is typically low signal on T1 and has high marrow signal on STIR and T2 images (6). It is considered to be the most sensitive modality. The sensitivity is relatively high, ~85%. MRI has improved soft tissue resolution, multiplanar abilities, and provides guidance for tissue sampling.
Sensitivity Specificity
Radiography 67% 40%
3-Phase Bone Scan 85% 54%
Gallium Scan 81% 69%
In-111 Leukocyte Scan 100% 70%
MRI ~85% -

Conclusions

Current imaging recommendations include radiographs followed by a three phase bone scan or and MRI if available. Additional imaging with Indium-111 leukocytes and gallium is used as needed (7). Gallium seems especially valuable in monitoring the efficacy of treatment.

References

1. Loredo R, Metter D,: Imaging of the diabetic foot, Emphasis on nuclear medicine and magnetic resonance imaging. Clinics in Podiatric Medicine and Surgery 14(2): 235-264, 1997.

2. Lipman BT, Collier BD, et al: Detection of osteomyelitis in the neuropathic foot: nuclear medicine, MRI, and conventional radiography. Clinical Nuclear Medicine 23(2): 77-82, 1998.

3. Gold RH, Tong DJF, et al: Imaging the diabetic foot. Skeletal Radiology 24: 563-571, 1995.

4. Johnson JE, et al: Prospective study of bone, Indium-111-labeled white blood cell, and gallium scanning for the evaluation of osteomyelitis in the diabetic foot. Foot and Ankle International 17(1): 10-16, 1996.

5. Schauwecker DS et al: Evaluation of complicating osteomyelitis with Tc-99m MDP, In-11 granulocytes and Ga-67 citrate. Diagnostic Nuclear Medicine 25(8): 849-853, 1984.

6. Yuh, WT, et al: Osteomyelitis of the foot in diabetic patients: evaluation with plain film, Tc-99m ­MDP bone scintigraphy, and MR imaging. AJR 152: 795-800.

7. Becker W: Imaging osteomyelitis and the diabetic foot. The Quarterly Journal of Nuclear Medicine 43(1): 9-17.

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J. Anthony Parker, MD PhD, Tony_Parker@CareGroup.Harvard.edu