Diabetic foot infection and MRI

A 62-year-old patient with type 2 diabetes of 3 years' duration developed an ulcer of the right 1st toe which had been present for 6 months when first seen in the foot clinic. He then had cellulitis and a markedly swollen 1st

(Fig. 5.14a,b). This indicated osteomyelitis of the metatarsal head.

There was a small collection of fluid between the extensor hallucis longus tendon and the metatarsophalangeal joint/proximal phalanx of the big toe (Fig. 5.15a-c). The decision to debride the foot and carry out a 1 st ray amputation was difficult but in view of the resolution of his fever and the improvement in the soft tissues clinically, intravenous antibiotic therapy was continued and the patient's ulcer eventually healed without surgery (Fig. 5.15d).

Key points

• It is difficult to diagnose osteomyelitis in the cellulitic foot as the X-ray is often initially normal

• MRI can indicate signs of marrow oedema which suggest osteomyelitis

Image Not Available • Group B Streptococcus is an important pathogen in the diabetic foot. It may need aggressive treatment with high-dose penicillin therapy such as amoxicillin 1 g tds. In severe cases, gentamicin 5 mg/kg daily can be added for synergy

• Osteomyelitis may be managed conservatively, especially when the soft tissue sepsis is responding to intravenous antibiotic therapy.

Fig. 5.14 (a) T1 sequence shows reduced signal in 1st metatarsal head compared with other metatarsal heads, (b) Increased uptake on STIR sequence in 1st metatarsal head compared with other metatarsal heads. (Courtesy of Dr David Elias.)

toe. X-ray was normal. Deep wound swab revealed Streptococcus group B. He was treated with amoxicillin 500 mg tds and gentamicin 5 mg/kg daily, both intravenously. The temperature resolved but the cellulitis was slow to improve. Because of the persistent swelling of the right 1st ray, the patient underwent an MRI to assess the presence of osteomyelitis and a possible collection of fluid. The images were Tl, and STIR and T1 postgadolinium with fat suppression to assess presence of fluid collections. There was oedema within the marrow of the head of the 1st metatarsal. There was cortical loss on its volar aspect and enhancement of the marrow in this region

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