A Charcot joint may have severe consequences, but is difficult to diagnose

In his previous article on diabetic foot ulcers, Dr Bobby Huda – consultant in diabetes and metabolism at St Bartholomew’s and Royal London Hospitals –discussed the aetiology of diabetes foot ulcers and possible consequences. In this follow-up article he looks at issues surrounding Charcot foot: a specific clinical scenario that requires further discussion.

JEAN-MARTIN CHARCOT was a French neurologist and a professor of anatomical pathology in the mid part of the 19th century. He described a number of conditions, among which was the Charcot joint or Charcot arthropathy (or neuroarthropathy). This is the progressive degeneration of a weight-bearing joint seen in individuals with significant peripheral neuropathy. It can be seen in people with any cause of peripheral neuropathy.

In the 19th century, leprosy and syphilis were common underlying causes; however, with the decline of those conditions it is now most commonly seen in people with diabetes.

Epidemiology and pathophysiology

The incidence varies between 0.1 to 0.4% in people with diabetes, but the prevalence can be up to 35% of people with peripheral neuropathy. People with Charcot’s neuroarthropathy (CN) are usually in their fifth or sixth decade, and have had diabetes for 10 years or more.

It is more commonly unilateral, but can be bilateral in later stages. The underlying pathophysiology is not fully understood, but it is likely to involve alterations to blood flow to the foot caused by nerve damage, repeated minor trauma in the presence of neuropathy and an inflammatory bone response. The consequence of those different pathways are small microfractures within the foot bones, an inflammatory response and eventually destruction of bone and joint architecture.

Clinical presentation

CN usually affects the foot and ankle joints but can be in other areas, such as the knee. The foot is warm, reddened and swollen. That, however, is also common in other pathologies such as cellulitis (infection in the soft tissue), ankle sprain, deep venous thrombosis and inflammatory arthritis. The patient may or may not have pain associated with it. The increase in foot temperature can be measured by podiatrists and can be useful in monitoring response to therapy. That is the acute presentation of CN, but it can settle into a more chronic phase, where the destructive process can continue at a slower rate or stay relatively stable.

Investigations

CN is primarily a clinical diagnosis and hence it can be difficult to diagnose. The erythrocyte sedimentation rate (ESR) or C-reactive protein may be raised. X-rays may be normal in the first few weeks, but over time they can show inflammation, soft tissue oedema and evidence of fractures and bone destruction.

Magnetic resonance imaging (MRI) is the most sensitive imaging modality for detection of early CN, and soft tissue/bone oedema are often seen. Nuclear medicine uptake, white cell uptake and PET scans are used in specialist centres occasionally, particularly where they are needed to differentiate from osteomyelitis.

Treatment

The mainstay of treatment for CN is offloading the foot, so as to minimise further trauma. This can be done with an aircast boot, which is advantageous in that they can be easily applied, are commonly available and easy to remove for comfort, or to monitor progress or an accompanying ulcer. The disadvantage is that they are not bespoke for the patient – so may not be an ideal fit – and most importantly the patient can remove it, so subsequently may be without the treatment for several hours in the day. The gold standard of treatment is a total contact cast (TCC), which is bespoke for the patient’s foot architecture and is not removable. However, TCC needs skilled specialist staff, close monitoring – to avoid ulceration if poorly fitting – and is not available in all centres. Although there have been clinical trials of the use of medical treatment such as bisphosphonates, there has been limited evidence of benefit. Glucose control should be optimised and accompanying infection/ ulceration treated. Surgery can be used in chronic CN to reduce bone deformity and stabilise the foot, but is done only in specialist centres and is not commonly used.

Prognosis

Without prompt detection and treatment, people with CN will go on to develop bone deformity, ulceration and eventually the bone architecture of the foot can collapse, leading to a below knee amputation. In world-class specialist centres, with prompt referral and treatment, prognosis can be good, with 94% of patients walking independently.

Pitfalls

However, CN is misdiagnosed in 95% of cases and in a survey of non-foot specialist providers 70% had a self-described poor or complete lack of knowledge of the condition. The consequence of delayed diagnosis can be catastrophic, with one study showing a 9.1% chance of a complication (fracture/severe deformity) after a one month delay in referral, and a 92.3% chance of a complication with a three month delay. Unfortunately, real world data shows that the average time between symptoms and treatment is 21 weeks.

The condition, however, is relatively rare, with most general practitioners in the UK usually only seeing 1-2 cases in their career. It is commonly misdiagnosed as cellulitis or a deep vein thrombosis. That leads to several weeks without offloading and progression of the destructive process. Ideally, patients with CN would be detected early and promptly referred to a specialist diabetes foot clinic. National Institute of Clinical Excellence NG19 guidelines recommend that people with suspected CN are referred to a diabetes foot multi-disciplinary team within one working day, but the National Diabetes Foot Audit shows that only 13% of patients are seen within two days of referral.

Medico-legal aspects

Most claims will centre on a delay in diagnosis and referral to a specialist centre. Cases for claimants will highlight the consequences of delayed diagnosis and treatment, which as above can be seen as causative for many complications. The defendant’s case can centre on the relatively rare nature of the condition and that many peers would also have poor knowledge of the condition. q

• To contact Dr Huda call 020 3594 6058 / 07919 924925, email bobby.huda1@nhs.net alternatively visit londondiabetes.com or clevelandcliniclondon.uk