Charcot foot

The patient with diabetes presenting with a hot foot is not an uncommon event for all health care professionals, based in either primary or secondary care and whether they have an interest in diabetes or not. There does seem to be a knee jerk reaction to these patients where infection is considered as the only likely cause yet failure to respond to antibiotics does not always ring alarm bells of another chronic and serious condition, the Charcot foot. Chronic neuropathic osteoarthropathy (Charcot) is a condition affecting the bones, joints and soft tissue of the foot and ankle. Its aetiology is uncertain but usually occurs in the presence of diabetic neuropathy (sensory, motor & autonomic). Mild trauma, often unrecognised by the patient, increased peripheral blood flow and metabolic abnormalities of the bone all result in an acute inflammatory condition eventually leading to bone destruction, dislocation and deformity. Left untreated the hallmark chronic deformity, commonly known as a rocker bottom foot commonly lead to long term problems including recurrent ulceration.

The key to management of this condition is early recognition especially in the presence of neuropathy. The patient who may have little recollection of trauma usually has bounding peripheral pulses and a marked temperature difference between the feet. As well as infection, thrombosis, gout or fracture are also in the differential yet easily excluded. Inflammatory markers may not be significantly raised. Initial imaging via a plain X-ray is often unhelpful, whilst an MRI may show early subtle changes and is usually the investigation of choice. Isotope bone scans may also show increased bone metabolic activity.

From a primary care point of view, management is simple – these patients should be referred urgently to a specialist diabetic foot clinic, ideally urgently as early management is essential in reducing the risk of long term deformity. Offloading during the active stage of the Charcot foot is the most important management strategy. Ideally, the foot should be immobilised in a total contact cast (TCC) – usually plaster – which is replaced after a few days following resolution of any oedema. This immobilisation is continued until the temperature in the affected foot is within 2^oC of the contra lateral foot. A walking cast is often used instead of TCC. This has the advantage of being removable for easy assessment although there does need to be confidence in the patient’s ability to keep such a cast on at all times. Many foot clinics also use anti-resorptive agents such as intravenous or oral bisphosphonates at the time of diagnosis although the evidence for this is variable. Finally, orthopaedic surgery does have its place in correcting any anatomical abnormalities but only when the active phase has settled. Bespoke orthotic footwear plays a significant part in long term management to promote offloading and reduce the risk of ulceration in a deformed foot. Long term surveillance is required after the foot has settled to monitor for signs of recurrent or new Charcot episodes as well as other diabetic foot complications.

The Charcot foot is often the Cinderella of diabetic foot disease requiring a high index of suspicion. Early referral and treatment is usually the key to prevent long term deformity and recurrent foot problems.

Dr Mark Freeman

March 2015