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The Foot Complications of Diabetes: Everything You Need to Know

Well, perhaps not everything, but quite a lot (!) Both type 1 and type 2 diabetes can have a significant impact on the feet. Complications primarily result from high (poorly controlled) blood sugar levels which damage the nerves (neuropathy) and blood vessels in the feet. There are an estimated 4.5 million people with diabetes in the UK alone. Foot problems are not inevitable. The chance of developing complications associated with diabetes can be minimised by carefully managing blood sugar levels and promptly seeking help via your GP, practice nurse or podiatrist if any change of sensation is noted.

Peripheral Neuropathy This is a common complication of diabetes; the prevalence of peripheral neuropathy in the diabetic population ranges from anywhere between 6% - 70% according to online sources. Peripheral neuropathy is damage to the nerves in the feet (actually to all peripheral nerves, but for the purpose of this blog we're just discussing the feet), leading to a change of sensation. As symptoms progress, the individual may not feel e.g. pain, heat or cold, thereby making the person more vulnerable to cuts, blisters, and other injuries, and loss of proprioception (the ability to sense where your limbs are in space) and reduced/lost sensory feedback will cause alterations to a person's walking style (e.g. a 'stomping' gait in sensory ataxia).

As in all diagnoses, there is a spectrum here. Some folks may have a general feeling of 'walking on pebbles' or occasional tingling, but their protective sensation is intact i.e. if they stubbed their toe, or their shoe was rubbing - they'd feel it. Plus it's worth noting that these early changes in sensation may not be caused by diabetes in isolation - has the person recently taken up a vegan or vegetarian diet rendering them B12 deficient? Are they a bit of a boozer, or at least, have they been lately? (An excess of alcohol leads to malabsorption of B12 in the gut). Why is B12 Important? B12 (cobalamin) holds many functions in the human body (I will discuss this in a separate blog post) but in the context of diabetes, nerves and foot problems, B12 is essential for maintaining a healthy nervous system. Certain nerves are wrapped in a fatty membrane (myelin sheath) that helps to transport signals more quickly around the body - B12 is required in the formation of this membrane.

Clinicians should explore all options in order to ascertain the cause of the change of sensation and prevent further deterioration. This is especially important at the early stages of any change; is the blood sugar running too high at the moment? If so, why? Is it affecting the person's sleep? If so, a low dose antidepressant (amitriptyline) can be prescribed with - anecdotally at least - good effect (even if the evidence doesn't tally with this). Something that has always foxed me is that the number one drug in the treatment of type 2 diabetes - Metformin - is known to leach B12 from the cells; therefore - in essence - advancing the chance of peripheral neuropathy. The professional word on this is for patients on Metformin 'at risk of deficiency' to have their B12 levels tested 'at intervals'. Trouble is, once you are clincially B12 deficient - that's it. Surely it would be more sensible to prescribe a B12 supplement on commencement of Metformin? Sadly preventative medicine isn't seemingly how we roll in the UK. It's worth noting that running your blood sugars too low (hypoglycaemia) can also cause nerve damage. Good glycaemic (sugar) control requires a finely tuned balancing act.

And - fun fact - the medication prescribed to help prevent furring of the arteries in diabetes (statins), can also cause peripheral neuropathy (as a 'rare or very rare' side-effect).

Reduced Blood Flow High blood sugar - that is, too much sugar roaming around your body and not being utilised or stored in muscles - will damage blood vessels. The sugar molecules not only stick to the vessel walls, but also to the actual blood molecules - making them heavier, claggier, if you will (is this a word? Not sure), so that the blood is slower to flow through the vessels. This reduction of flow can starve the blood supply to the nerves (contributing to peripheral neuropathy), cause skin changes, and impede healing. In very severe cases, this can lead to cell death and gangrene (necrosis). There is also an as-yet-not-fully-known mechanism which leads to furring of the arteries in diabetes (atherosclerosis). The link, however, is undisputed and is the reason why patients are typically prescribed a statin.

Ginkgo biloba is a supplement indicated to improve circulation, though I could not find any studies to support this (although there are a huge number out there investigating whether ginkgo can improve blood flow to the brain, and certainly this brain health expert highly recommends it).

Foot Ulcers A foot ulcer is a wound that takes a long time to heal (typically more than 6 weeks). One could start innocently enough through the rub of a shoe. This is why when a person is diagnosed with diabetes, the message is hammered home that they must check their feet every day. And really, this cannot be overstated. Ulcers can become infected - in fact, a person with diabetes is more prone to infection - and may require intensive treatment. What does this actually mean? Well, potentially two or three appointments a week with a specialist podiatrist plus antibiotics, blood tests, not being able to wash properly (the dressings need to be kept dry), alterations to footwear and activity levels; which comes with it's own trade-offs; you need to be on your feet less to help heal the ulcer, meanwhile you're potentially gaining weight, your blood sugar is soaring, you feel down as you can't see your friends and family as much and you are becoming increasingly immobile through inactivity ('use it or lose it'). An estimated 10% of people with diabetes will develop a foot ulcer at some point in their lives.

This is something that can escalate VERY quickly. If you are diabetic and notice there is a new graze, blister or rub to your foot, cleanse the area with some warm saltwater, pat dry with some sterile gauze (or equivalent), apply a clean, dry dressing and contact your GP or foot service ASAP. In some areas you can self-refer to podiatry if you have a foot problem (in Oxfordshire you can here).

Charcot Foot This is rare (about 1% of people with diabetes and neuropathy will be affected) - but it is worth knowing about. This tends to affect individuals with established peripheral neuropathy and presents as a hot, red, swollen foot - with or without pain. The bones in the foot become more brittle (this is related to the altered blood flow in the feet. For a full explanation read this) and can collapse. It can be mistaken for an infection, sprain, gout or a fracture - which is the main cause for a delay in treatment. In order to minimise damage, a Charcot foot should be immobilised ASAP. To give an example of how this can occur, I saw a gentleman with type 2 diabetes in a community clinic complaining of pain in his neuropathic foot (i.e. he didn't usually feel pain). He had been digging in his garden with a spade - the pressure of applying his senseless midfoot to a spade into hard ground will have been enough to damage the soft bone in his foot and commence the cascade of inflammation and destruction that is a Charcot foot. Early signs can be missed on x-ray; an MRI is the preferred diagnostic tool here.

Infections We've touched on this already, but suffice to say that if you have diabetes you are more prone to infections and they can take longer to heal. This is all types of infections - bacterial, fungal, yeast... so if you've spotted a hot/red/swollen bit (see image below) or a little sliver of fungal infection on a nail it's worth nipping that in the bud PDQ. What does an infection look like?

Gangrene Severe infections and poor blood flow can lead to tissue death (gangrene, necrosis). In some cases, amputation may be necessary to prevent the spread of gangrene. More than 7000 diabetes-related amputations are reported in the UK per year.

Foot Deformities Relating to those softer bones we mentioned earlier, plus motor neuropathy (damage to the nerves that control the muscles) which can lead to clawing of the toes, and a high arch (pes cavus) which in turn alters the distribution of pressure across the feet. Hightened pressure can cause to callus (hard skin) build up, callus in the absense of sensation (peripheral neuropathy) can lead to ulcers. Additionally, the foot shape can change so that shoes that once fitted well are no longer suitable. Keep an eye out for new rubs (tops of toes, sides of the feet) or calluses - or corns that were not there before.

Skin Changes

Diabetes can cause skin changes in the feet through a number of mechanisms; that excess sugar? This can stick to the cells, affecting cell turnover and causing plaques of thick skin to form. Damage to the nerves can prevent the sweat glands from working (our natural moisturiser) - autonomic neuropathy - which dries out the skin and can cause cracks. The cracks (fissures) can be deep and become infected. Diabetic dermopathy is harmless, but can alter the appearance of the skin. We've mentioned changes in foot shape causing new pressure areas which can lead to thickened skin (callus) and corns. It's imperative to use an emollient (moisturiser) reguarly (preferably daily) to help ameliorate these symptoms. As a rule of thumb, anything containining urea is a good option - although some patients can be sensitive to this. Any moisturiser is better than no moisturiser at all - so the basic recommendation is to go with anything you will actually use!

Take Home Messages To prevent or manage these complications and protect your feet when you have diabetes, it's important to:

- Maintain good blood sugar control through diet, exercise, and medication as prescribed by your GP or consultant.

- Check your feet daily for any injuries, blisters, hard skin or other changes in skin condition,

- Practice good foot hygiene, including regular washing and moisturizing (avoiding between the toes - can get a bit soggy in there).

- Wear good shoes that provide adequate support; ie a toebox that is wide and deep enough to accommodate your foot shape, a decent sole and a fastening (e.g. laces or velcro). Slip on shoes are never a good choice. For anyone!

- If you have lost protective sensation in your feet, avoid going barefoot to prevent injuries.

- Seek regular foot exams and care from a suitably qualified healthcare professional or podiatrist. A neurovascular assessment to check protective sensation and blood flow should be performed annually by a podiatrist or at your GP practice.

Need to find a podiatrist? Registered and insured degree-qualified podiatrists can be found on the Royal College of Podiatry and Institute of Chiropodist & Podiatrist's websites.

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