A 57-year-old obese male patient with type 2 diabetes diagnosed at the age of 40 years was referred to the outpatient diabetic foot clinic because of a chronic ulcer under his right foot. He was being treated with insulin and metformin with acceptable diabetes control (HBAic: 7.8%). He had a history of background retinopathy and cataract in both eyes. He reported a severe deep tissue infection 5 years earlier after a burn sustained under his right foot. At that time he was hospitalized for about 1 month and treated with intravenous antibiotics and surgical debridement.
On examination, the patient had severe diabetic neuropathy with loss of sensation of pain, light touch, temperature, vibration,
Figure 8.26 Healing of the ulcer affecting the foot shown in Figures 8.23-8.25. This photograph was taken 3 months after that shown in Figure 8.25
and 5.07 monofilaments. Achilles tendon reflexes were absent. The vibration perception threshold was above 50 V bilaterally, while the peripheral pulses were normal. A scar was noted on the dorsum of his right foot which had an overriding fourth toe, as a result of past surgical procedures. A full-thickness neuropathic ulcer was present under his fourth metatarsal head surrounded by callus (Figure 8.27).
A bony prominence could also be felt under the ulcerated area. A plain radiograph did not show osteomyelitis or neuro-osteoarthropathy. Debridement of the ulcer was carried out and extra depth therapeutic shoes with a flat insole were prescribed (Figure 8.28); a window was made in the insole in order to offload pressure on the ulcerated area; the ulcer began to heal well (Figure 8.29).
The patient kept himself very active. He returned to the clinic after 3 weeks absence with a deeper ulcer involving the tendons (Figure 8.30). The underlying bone could not be detected with a sterile metal probe and a plain radiograph did not show osteomyelitis. An elevated erythrocyte sedimentation rate (74 mm/h) and mild leuko-cytosis were found, therefore the possibility of osteomyelitis was high. A magnetic resonance imaging-T1-weighted sagittal image of the foot was obtained, showing a phlegmonous mass starting from the skin and extending to the deeper tissues causing erosion of the fourth metatarsal head (Figure 8.31). The patient was hospitalized so that offloading pressure from the ulcerated area was enforced, and intravenous antibiotics were administered. Two weeks later the size of the ulcer had decreased by almost 50%.
Several methods are used for the diagnosis of osteomyelitis. Probe-to-bone tests (contacting the bone with a sterile metal probe) have a sensitivity of more than 90% and they are carried out at the bedside. Plain radiographs have a sensitivity of 55%, but when repeated—usually
2 weeks later — the sensitivity is higher, making this the most cost-effective diagnostic procedure. Computerized tomography may reveal areas with subtle abnormalities such as periosteal reactions, small cortex erosions and soft tissue abnormalities. Magnetic resonance imaging has a sensitivity of almost 100% and a specificity of over 80% and has the potential to reveal abscesses. Therefore this is the preferred method for the diagnosis of osteomyelitis in many centers in cases where the plain radiographs do not provide sufficient information to make a conclusive diagnosis. However, the specificity of MRI decreases in the presence of neuro-osteoarthropathy, prior bone biopsy, recent bone fracture or recent surgery. Magnification radiography is also a very useful method for the detection of early osteomyelitis and it is used to follow up the disease.
Bone scintigraphy imaging is explained in Figure 8.37.
Keywords: Neuropathic ulcer; magnetic resonance imaging; MRI; osteomyelitis; diagnostic methods for osteomyelitis
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