Infection can also present as a bluish-purple discolouration when there is inadequate supply of oxygen to the soft tissues.
This is caused by increased metabolic demands of infection and a reduction of blood flow to the skin,
Fig. 5.10 (a) Callus has been debrided and ulceration appears to be shallow, (b) Palpation extrudes a bead of pus from deep in the heel, (c) Surgical debridement of infected tissues, (d) The foot healed after surgical debridement.
secondary to a septic vasculitis of the cutaneous circulation. Blue discolouration can occur in both the neuropathic and also the neuroischaemic foot, particularly in the toes, and in the neuroischaemic foot must not be automatically attributed to worsening atherosclerosis.
In very severe cases of cellulitis, bluish-purple or black discolouration of the skin develops with blistering. Purple blebs may indicate subcutaneous necrosis. A probe can often be inserted deep into the foot.
Fig. 5.10 (a) Callus has been debrided and ulceration appears to be shallow, (b) Palpation extrudes a bead of pus from deep in the
Systemic symptoms and signs may be present in the patient whose foot has extensive diffuse cellulitis, deep soft tissue infection or blue discolouration. However, systemic signs and symptoms are notoriously absent in many severe infections of the diabetic foot. Among patients hospitalized for severe infections only 12-35% have significant fever and only 50% of episodes of severe cellulitis will provoke a fever or leucocytosis. However, when a fever is present it usually indicates a severe heel, (c) Surgical debridement of infected tissues, (d) The foot healed after surgical debridement.
infection. The deep spaces of the foot are usually involved with tissue necrosis, severe cellulitis or bacteraemia.
Other warning signs of severe infection which may or may not be present include:
• An unusually drowsy patient
• A patient who is shivering.
Severe subcutaneous infection by Gram-negative and anaerobic organisms produces gas which may be detected by palpating crepitus on the lower limb and can be seen on X-ray. The presence of gas does not automatically mean that the classical gas gangrene organism Clostridium perfringens is present. The most common cause is either Gram-negative organisms or other anaerobes.
Any of the above five presentations may be complicated by underlying osteomyelitis.
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