PET-MRI in diagnosing pedal osteomyelitis in diabetic patients

Objectives Osteomyelitis of the foot is a serious complication that requires accurate diagnosis and prompt treatment in diabetic patients. Magnetic resonance imaging (MRI) of the foot has been shown to be the most accurate imaging modality with a high sensitivity and negative predictive value but slightly lower specificity. FDG-PETused in conjunction with CT has been shown to have a lower senstivity but higher specificity than MRI.

Methods Retrospective review of imaging was performed in seven consecutive patients who underwent PET-MRI of the foot for a clinical suspicion of osteomyelitis. The MR imaging findings were graded as Grade 0 - normal signal, Grade I - hazy reticulated, T1 hypointense signal, Grade II - confluent T1 hypointense signal. Grade II, confluent hypointense marrow signal was considered diagnostic of osteomyelitis. Reticulated hazy signal was deemed to reflect edema on MRI. FDG uptake localizing to the bone on fused PET-MRI images was diagnosed as osteomyelitis. Five of the seven patients (71%) subsequently underwent surgery. Two patients diagnosed with osteomyelitis opted for conservative therapy.

Results All seven patients were diagnosed as osteomyelitis on PET- MRI. Five patients had osteomyelitis on histopathology and 2 patients according to secondary clinical end points. Three cases with FDG uptake involving the bone on fused images had negative MRI patterns (Grade I reticulated T1 hypointense signal or no signal change). All the cases positive on MRI were positive on FDG-PET. MRI component increases the reader confidence and accurate anatomic localisation of abnormality. The sensitivity of PET-MRI to diagnose osteomyelitis was 100% in this small series of diabetic patients.

Conclusions PET-MR is highly sensitive modality with high reader confidence for diagnosis of osteomyelitis in diabetic foot.