Differential diagnosis of acute Charcots osteoarthropathy

A 65-year-old man with type 2 diabetes of 21 years' duration developed a hot, red, swollen left foot, after tripping in the street. On examination the foot was hot and swollen, particularly over the lateral aspect of the ankle. However, pulses were not palpable and the pressure index was 0.6. X-ray was normal. The differential diagnosis was an acute Charcot's osteoarthropathy or a soft tissue injury. Charcot's osteoarthropathy was thought to be less likely in view of the moderate ischaemia: however, it could not be excluded. The foot was put in a cast until an MDP bone scan was performed. This showed a diffuse uptake around the left ankle but no focal bony change, indicating a soft tissue injury (Fig. 3.17a,b). The patient was mobilized without a cast and the swelling gradually resolved.

Key points

• Patients presenting with a hot swollen foot should be regarded as having a Charcot's osteoarthropathy until proved otherwise

• Until an MDP bone scan can be performed, the foot should be casted

• The MDP bone scan can differentiate between soft tissue and bony damage.

Differential diagnosis of acute onset Charcot's osteoarthropathy

It is important to differentiate between the red, hot,

Fig. 3.17 (a) MDP bone scan showing diffuse uptake around the left ankle, (b) Normal X-ray of left ankle.

swollen appearance of Charcot's osteoarthropathy and the red, hot swollen cellulitic foot. Cellulitis is more likely in the presence of an ulcer which may show typical signs of infection. Infection severe enough to cause generalized redness, warmth and swelling will usually cause local signs such as discolouration of the bed of the wound, and discharge from the ulcer. The swelling of Charcot's osteoarthropathy responds more rapidly to elevation than does that of the infected foot. Infection and Charcot's osteoarthropathy can sometimes be present concurrently in the same foot. If in doubt, treat for both.

Gout and deep vein thrombosis may also masquerade as Charcot's osteoarthropathy but can be excluded by measurement of serum urate and duplex vein scan.

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