Diabetic Foot Infection: A Major and Dangerous Complication of Diabetes Mellitus

Diabetic foot infections are major and dangerous complication of diabetes mellitus. The ulceration of foot with infection can lead to tissue necrosis and amputation. It is a leading non-traumatic cause of major amputation of the lower limbs.Foot in diabetic patient is prone to ulceration, trauma and infection due to peripheral neuropathy, peripheral vascular disease, glucose rich environment and impaired resistance. High glucose level in tissues is a good culture media for bacteria therefore infection is common.

It can be neuropathic, ischaemic or neuroischaemic. About 20 - 40% of patients have neuropathy while 50% will develop symptomatic pheripheral vascular disease within 20 years of diagnosis. About 15% in diabetic mellitus have the lifetime prevalence of foot ulceration.The Charcot foot can lead to significant bone destruction, deformity and ulceration.

Due to sensory neuropathy, the protective sensations of pain, heat and pressure are lost. Minor injuries are not noticed by diabetic patient and so the infection occurs. Due to motor neuropathy dysfunction of muscles, arches of foot, joints and loss of reflexes cause more prone to trauma and abscess. Due to autonomic neuropathy skin is dry causes defective skin barrier so more prone to infection.
Ischemia is due to accelerated atherosclerosis in large vessel (usually in the femoral, popliteal and tibial arteries) and structural and functional abnormalities of the micro-vascular endothelium. The skin of foot is red, dry and thin, and susceptible to breakdown on minor trauma.

Some contributing factors are also responsible to the onset of ulceration of foot in diabetic patients in addition to neurovascular disease like poor vision, cerebrovascular disease, limited mobility in the joints and peripheral oedema due to coronary heart disease.

Clinical assessment of the foot at-risk

Neuropathy is detected by
1. Testing vibration by using a biosthesiometer or tuning fork.
2. Discriminatory touch using a 10-g monofilament.
3. Assessing the ankle jerks.

Vascular examination
1. Palpation for dorsalis pedis, posterior tibial, popliteal and the
femoral  pulses.

2. Skin colour and temperature.

3. Strength of pulsation
4. Presence of abdominal and femoral bruits.

Risk factors
1. Glycaemic control
2. Duration of diabetes
3. Renal disease
4. Cigarette smoking
5. Poor social circumstances.

Monitoring and self care are key parts of management. 3-6 monthly review should be done. Patient education includes

• Washing
• Inspection
• Care of corns and calluses
• Toenail cutting
• Wearing suitable footwear
• Keep your feet as clean as your face
• Ablution (Wazoo) five times a day in Muslims

The ulcerated foot

May be intrinsic defects in the ulcer healing in diabetic patients

• Impaired fibroblast function
• Deficiency in growth factors
• Abnormalities found in the extra cellular matrix

Therefore delayed foot wounds healing and prolonged hospital stay is common.

Neuropathic ulcers which are associated with the callus, which develops on the plantar aspects of the metatarsal heads.
Neuroischaemic ulcers which are common on the margins of the diabetic foot.

Infection is divided in to

• Local and superficial
• Spreading soft tissue infection and the cellulitis 
• Osteomyelitis

The signs of inflammation and early infection in foot may be difficult to detect in the presence of peripheral vascular disease. 

Deep wound swabs often show the presence of several bacteria (Gram +ve, Gram -ve, aerobic and anaerobic organisms). Antibiotics should be used accordingly.

Osteomyelitis is a common sequela of diabetic foot ulceration, usually caused by staphylococcus aureus. Plain x-rays of all patients of diabetic foot ulcers should be done. MRI when osteomyelitis is suspected.
Duplex ultrasound of lower limb is done for diabetic ischaemic ulcer.
Surgery (Debridement or amputation) is needed when antibiotics failed.