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Diabetic foot
People with diabetes are more prone to infection. They can also develop neuropathy (damaged nerves) or peripheral vascular disease (blocked arteries) of the legs and either can lead to foot ulceration.
Infection and foot ulceration, alone or in combination, often lead to amputation. Neuropathy and peripheral vascular disease can also cause distressing pain in the lower limbs.
Diabetes-related foot problems like osteomyelitis and Charcot neuro-osteoarthropathy are associated with a high morbidity and high healthcare costs.
Osteomyelitis in a diabetic with neuropathy is infection of the bone that usually results from contiguous spread of a skin ulcer. Consequently, the most common location for osteomyelitis is not in the midfoot, but at the pressure points of the forefoot (metatarsal heads, IP joints) and in the hindfoot at the plantar aspect of the posterior calcaneus. To determine whether osteomyelitis is present, is to place a marker on the ulcer or sinus tract and track it down to the bone and evaluate the MR- signal intensity of the marrow .
The MRI examination includes special attention for positioning of the foot. It must be placed in the centre of the magnet, to obtain homogeneous fat suppression. Markers have to be placed over ulcers or sinus tracts. T1 and STIR or T2 fatsat sequences are needed. Because of the curvature of the foot, fat suppression is more uniform with the use of STIR than with T2- weighted imaging with chemical fat saturation.However, SIR cannot be combined with contrats administration. As an alternative to spectral fat saturation technique, Dixon chemical shift imaging is described .
Sagittal views are for evaluation of midfoot involvement, the plantar surface and the posterior calcaneus. A view parallel to the toes is adequate for imaging the metatarsophalangeal and interphalangeal joints. Contrast is used to better depict devitalized regions, abscesses, sinus tracts and joint or tendon involvement.
Diabetic neuropathy means damage of nerve fibres in people with diabetes. How the nerves are injured is not entirely clear but research suggests that high blood glucose changes the metabolism of nerve cells and causes reduced blood flow to the nerve. There are different types of nerves in the body. These can be grouped as :
Neuropathy can result in two sets of what superficially appear to be contradictory problems. Most patients who have neuropathy have one of these problems but some can be affected by both.
A typical neuropathic ulcer is shown in the figure below. Patients with neuropathy lose their sensation of pain. As a result, they exert a lot of pressure at one spot under the foot when they walk, building up a callus at that site without causing discomfort. The pressure becomes so high that eventually it causes breakdown of tissues and ulceration. The patient hardly notices any pain.
A typical neuropathic ulcer is :
Please note if neuropathic ulcers occur elsewhere in the foot, it is usually due to footwear that is too tight. This image is of a neuropathic ulcer caused by shoe straps that were too tight.
The wounds of patients with severe vascular disease heal poorly because of inadequate blood supply. Therefore minor trauma or pressure often leads to ulceration. This is called a vascular ulcer (sometimes also known as arterial ulcer or ischaemic ulcer). It tends to be situated on the edge of the foot or toes because blood supply is the poorest at these sites. A typical vascular ulcer is shown below. In a purely vascular ulcer, nerve function is normal and sensation is intact, hence vascular ulcers are usually painful.
A typical vascular ulcer is :
A vascular ulcer should not be confused with a venous ulcer which is due to varicose veins. Varicose ulcers are situated on the leg (rather than in the foot), associated with varicose veins and often accompanied by swelling and a brownish discoloration of the leg. A typical varicose ulcer is shown bellow.