A 56-year-old woman presented with a two-week history of atraumatic left thigh pain and swelling. She had a background of poorly controlled type 2 diabetes with a recent HbA1C of 134mmol/mol (normal <40mmol/mol). She was afebrile and the rest of her vital signs were normal. Her left thigh was swollen and tender. There were no abnormal skin findings. Laboratory evaluation showed a normal white blood cell count. There was elevation of both CRP at 86mg/L (normal <5mg/L) and CK at 343U/L (normal 22–198U/L). Ultrasound and CT of the left thigh revealed a well-defined intramuscular fluid collection in the vastus lateralis. MRI findings are shown in Figure 1.

The considered differential diagnoses were diabetic myonecrosis, infectious myositis, necrotic neoplasm or abscess.

Figure 1: Coronal post-contrast T1 fat saturated MRI of the left thigh shows a hyperintense fluid collection and diffuse surrounding enhancement within the oedematous vastus lateralis muscle and subfascial fluid collection along the lateral surface.

Discussion

In the setting of this clinical presentation of a patient with poorly controlled diabetes without fever or leucocytosis, and supportive MRI findings, we made a diagnosis of diabetic myonecrosis. The diagnosis was reaffirmed by spontaneous clinical improvement and decreasing inflammatory markers without antibiotic treatment but only tighter glycaemic control. Therefore, we felt a biopsy was not indicated as it would not change management and would expose the patient to unnecessary risk of infection and haematoma. Outpatient follow-up at two weeks confirmed complete clinical resolution, and an ultrasound examination showed no residual collection and improved muscle architecture.

Diabetic myonecrosis, or diabetic muscle infarction, is a rare complication of diabetes.[[1]] This diagnosis should be considered in patients with poorly controlled diabetes presenting with acute onset of pain and swelling of the lower limbs, particularly in the thigh.[[2]] The pathogenesis is uncertain, but it has been attributed to microvascular thrombosis and ischaemia caused by endothelial damage.[[3,4]] Muscle biopsy is typically not required unless there is uncertainty regarding the diagnosis.[[5]] Short-term prognosis is good, but long-term prognosis is poor, which reflects the underlying severity of arteriopathy in these patients.[[6,7]] Estimated mortality from a major vascular event within two years after an episode of diabetic myonecrosis is reported to be 10%.[[8]] Treatment is conservative with a focus on diabetes control, analgesia and rest.[[1,9]]