Diabetic myonecrosis is a self-limiting disease that is rare, has an unclear pathogenesis, and most often affects the quadriceps muscle. This article reports a case of diabetic myonecrosis with poor glycemic control and was published online in the June 2015 issue of Diabetes Research and Clinical Practice. Case description The patient was a 59-year-old male with progressive severe pain in the left lower extremity for more than 2-3 weeks. The patient had no fever, rash, or arthralgia. There was no history of trauma. The patient had a history of type 2 diabetes mellitus for 2 years, which was poorly controlled with oral hypoglycemic medication. The patient was also diagnosed with proliferative retinopathy, chronic kidney disease stage 5, and erectile dysfunction. Swelling and tenderness of the distal left lower extremity was seen. The skin of the entire left lower extremity was erythematous. Pulses were palpable in both foot arteries. Left leg bending motion is limited. There is no exudate from the knee or hip joint. Laboratory tests: Creatinine kinase 649 U/L, elevated erythrocyte sedimentation rate 64 mm/h. Hemoglobin 98 g/L, white blood cell count 7.3×109/L. Screening for vasculitis and autoimmune disease negative. Serum urea was 22.2 mmol/L and blood creatinine 540 μmol/L, consistent with chronic kidney disease stage 5. HbA1c 74 mmol/mol (NGSP 8.9%), suggesting poor glycemic control. 2. Ultrasound examination of the left lower extremity showed diffuse subcutaneous edema. Vascular ultrasonography showed normal blood flow in the proximal iliac, femoral and N arteries, with only micro plaque formation. 3. MRI scan showed extensive swelling and edema of the left medial femoral, middle femoral and lateral femoral muscles, and also involved a small amount of the rectus femoris muscle, suggesting myositis or myonecrosis. The patient was initially diagnosed with infectious myositis and vasculitis necrosis, and was treated with antibiotics and prednisone, but the treatment was not effective, and further muscle biopsy was performed. The muscle biopsy suggested myofiber necrosis with localized regenerative fibrous tissue, suggesting long-term ischemia. The vascular appearance was normal and there was no evidence of vasculitis. Treatment The patient was eventually diagnosed with diabetic myonecrosis and was treated conservatively with pain medication and physical therapy, and glycemic control with insulin therapy. The patient’s muscle strength and left thigh function improved significantly during the treatment period, and edema was reduced. 3 months later, multiple MRI examinations showed a decrease in swelling and edema, with minimal signal changes remaining in the lateral and medial femoral muscles. Discussion Diabetic myonecrosis is a rare complication that has been reported in both type 1 and type 2 diabetes. Physicians should consider the possibility of diabetic myonecrosis in patients with poor glycemic control and sudden onset of nontraumatic limb pain. Risk factors for diabetic myonecrosis include long duration of diabetes and poor glycemic control. The prevalence is higher in women, at 61.5%. Patients usually have other associated microvascular complications, most commonly nephropathy. The most commonly involved muscles are: quadriceps (62%), hip adductors (13%), N cord (8%), hip flexors (2%) and, less commonly, gastrocnemius and upper limbs. 8.4% of patients have bilateral involvement. The cause of quadriceps as the main site of involvement is unclear and is presumed to be related to the long-term load level on this group of muscles. The clinical presentation is characterized by sudden onset of pain without systemic symptoms and without a history of trauma. Swelling, fever, and tenderness are present in the affected area. Hematologic studies show elevated creatine kinase (CK) and erythrocyte sedimentation rate (ESR) in 50% of patients. MRI imaging is an option and is characterized by low or equal signal on T1-weighted images and increased signal on T2-weighted images, suggesting edema. Enhanced MRI shows a central area of no signal enhancement with peripheral signal enhancement, suggesting central necrosis surrounded by surviving muscle fibers and inflammatory infiltrates. Muscle biopsy is not necessary routinely and may be considered when the diagnosis is unclear or when atypical presentations are present. Excisional biopsies should be avoided because of hematoma, infection, and delayed wound healing. After performing a muscle biopsy, the muscle biopsy shows large areas of necrosis and edema with involvement of collagen and granulation tissue. Perivascular and endomysial lymphohistiocytic infiltration has also been reported. Later, myofiber regeneration, mononuclear cell infiltration, and fibrosis are seen. The differential diagnosis includes septic myositis, necrotizing fasciitis, acute septal compartment syndrome, deep vein thrombosis, dermatomyositis, soft tissue abscess, primary muscle lymphoma, and sarcoma. Clinical and MRI examinations can differentiate them. Treatment Diabetic myonecrosis is usually a self-limiting disease and is usually treated with conservative therapy. The short-term prognosis is good, but the long-term prognosis is poor, with most patients dying within 5 years due to diabetic complications. Recurrence can occur in about half of the patients.