Diabetic foot pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Anahita Deylamsalehi, M.D.[2]Vishnu Vardhan Serla M.B.B.S. [3]
Overview
Pathophysiology
Diabetic foot is an umbrella term for foot problems in patients with diabetes mellitus. There are numerous responsible pathogenesis, such as arterial abnormalities, diabetic neuropathy, delayed wound healing and being more vulnerable to infection or gangrene of the foot. The key components of diabetic foot are neuropathy, ischemia and trauma. [1]
Neuropathy
- The most important cause of diabetic foot is neuropathy. Based on a study, more than 60% of cases of diabetic foot are due to neuropathy.[2]
- It involves roughly more than half of the patients with diabetes who are older than 60 years old.
- Peripheral neuropathy is usually profound at the point where it leads to formation of a foot ulcer.
- Some metabolic abnormalities due to hyperglycemia leads to ischemia of endoneurial microvessels. In a nutshell, these changes are most likely caused by a combination of factors listed below:
- High blood glucose
- Reactive oxygen species
- Vasculopathy
- Insufficient oxygenation of the nerves
- Presence of inflammation and autoimmunity due to diabetes
- Genetic factors
- Mechanical injury
- Smoking
- Alcohol abuse.
- Generalized symmetric distal polyneuropathy is the most common and widely recognized form of diabetic neuropathy that leads to diabetic foot. It may be either motor, autonomic or sensory, and can involve small fibers, large fibers or both.
- Motor nerve involvement:[3][4]
- Motor nerve involvement can lead to some mechanical changes in the foot of a diabetic patient due to loss of sufficient neural supply and alteration in natural anatomy of the foot. These mechanical changes cause more plantar pressure and higher risk of callus formation, which subsequently lead to higher rate of skin breakdown.
- Moreover, these anatomical changes usually result in wider and thicker foots, which no longer fit in patient's regular shoes and cause more trauma.
- Pathogenesis of some of these mechanical changes are listed below:
- Deprivation of neural supply to the intrinsic muscles of the foot → long flexor and extensor tendons imbalanced → flexion of the foot → high-arched foot and claw-toe deformity.
- Toes hyperextension → overriding of the metatarsal-phalangeal joints and downward displacement of metatarsal heads → Increased prominent of both.
- Toes hyperextension → distal displacement of metatarsal fat pads → altering the natural cushioning of these fat pads.
- Autonomic neuropathy:[5]
- Autonomic neuropathy leads to anhidrosis and impaired function of oil glands. The subsequent dryness of the skin results in higher chance of skin breakdown, ulcer formation and bacterial invasion.
- Autonomic neuropathy also decreases the proper peripheral sympathetic vascular tone which can leads to higher blood flow and pressure in distal arteries. The aforementioned changes plus capillary basement membrane destruction lead to edema. Edema itself increases the risk of ulcer formation.
- Sensory neuropathy:
- Appropriate sensory system helps patients to notice the tiniest fissures or blisters on their skin. This early sensation make it possible for patients to take care of these skin defects and prevent further complications.
- Conversely, diabetic patients with Sensory neuropathy are more prone to ulcer formation and related complications, since they don't feel pain with ever-deepening ulcers.
- Motor nerve involvement:[3][4]
Ischemia
- Atherosclerosis:[6][7]
- Atherosclerosis of the lower limb is 2 to 3 times more common in diabetic patients, compared to the normal population.
- Investigations reported that atherosclerosis in diabetic patients is more prominent in tibial and fibular arteries of the calf and arteries of the foot are relatively spared.
- It usually occurs due to inflammation and consequently leads to accumulation of the foam cells.
- Micro and macrovascular complications are one of the leading causes of diabetic complications. Microvascular complications cause skin damage, infection and impaired wound healing.[8]
- The vascular changes which are responsible for foot problems include stiff arteries due to calcification of the smooth muscle cells in the arterial wall (mediasclerosis). Consequently the stiff arteries are unable to expand in response to [[systolic pressure, which can lead to movement of plaques in calf arteries.[9]
- Most of these changes are discovered by an impaired ankle brachial index (ABI).
- The resting ABI is the ratio of the blood pressure in the lower limb to the blood pressure of the arms. It is calculated by dividing the systolic blood pressure of the ankle by the systolic blood pressure of the arm.
- It is a non-invasive method to assess the lower extremty arterial system and to detect the presence of arterial occlusion disease.
- Even in the presence of neuropathic foot ulcers, the reason of non healing wounds could be due to impaired blood supply to the tissue, which could be further augmented by antihypertensive medications.[10].
Trauma
- Trauma to the foot is frequently the trigger of diabetic foot ulcer development and repetitive trauma and pressure to the area prevent healing.[11]
- Excessive plantar pressure is related to limited joint mobility and foot deformities (such as charcot foot and hammer toe). Limited joint mobility and abnormal foot biomechanisms have been associated to an increased risk of ulceration.[10]
- Poor vision and sensory neuropathy further put diabetic patients at risk of foot ulceration, as they not feel the pain, nor do they see the ulcer. Loss of balance can also make patients more susceptible to falls.[10]
Defective hypoxic response
- A transcription factor named hypoxia‐inducible factor‐1 (HIF‐1), which become stable in hypoxia, functions as a oxygen homeostasis regulator.[12]
- Since HIF‐1 helps cells to response adequately to hypoxia (by regulating erythropoiesis, metabolic changes, angiogenesis, proliferation, migration, and cell survival), it plays a critical role in wound healing.[13]
- In addition, hypoxia‐inducible factor‐1 is responsible for expression of genes that are critical to facilitate wound healing, such as the GLUT1 and GLUT3, lactate dehydrogenase, genes responsible for proper mitochondrial function (such as phosphoinositide‐dependent kinase‐1), type I collagen and fibronectin. [14]
- There are numerous studies that detected lower level of HIF‐1 in biopsies of diabetic foot. [15][16][17]
- One of the known pathogenesis of destabilized hypoxia‐inducible factor‐1 is hyperglycemia. This destabilization in hyperglycaemic conditions has been explained by an increase in tendency of HIF‐1 towards VHL‐dependent degradation. [18]
Genetics
- Naturally growth factors and cytokines are two mediators involved in wound healing. It is crystal clear that any genetical changes that affect the aforementioned mediators can result in defective wound healing and higher chance of diabetic foot. The following are some known genetical changes:[19][20][21][22]
- A single nucleotide polymorphism (SNPs) is responsible in the variation of these growth factors and cytokines. The best known gene is MAPK14 located on chromosome 6.
- Decreased expression of certain cytokines and growth factors (such as IGF-1, TGF‐β1, PDGF, EGF, Interleukin 8 and Angiopoietin‐2)
Associated Conditions
Conditions associated with [disease name] include:
- [Condition 1]
- [Condition 2]
- [Condition 3]
Gross Pathology
On gross pathology, [feature1], [feature2], and [feature3] are characteristic findings of [disease name].
Microscopic Pathology
On microscopic histopathological analysis, [feature1], [feature2], and [feature3] are characteristic findings of [disease name].
References
- ↑ Assal JP, Mehnert H, Tritschler HJ, Sidorenko A, Keen H, Hellmut Mehnert Award Workshop Participants (2002). "On your feet! Workshop on the diabetic foot". J Diabetes Complications. 16 (2): 183–94. PMID 12039404.
- ↑ Grunfeld C (1992). "Diabetic foot ulcers: etiology, treatment, and prevention". Adv Intern Med. 37: 103–32. PMID 1557993.
- ↑ Younger DS, Rosoklija G, Hays AP (1998). "Diabetic peripheral neuropathy". Semin Neurol. 18 (1): 95–104. doi:10.1055/s-2008-1040865. PMID 9562671.
- ↑ Borssén B, Bergenheim T, Lithner F (1990). "The epidemiology of foot lesions in diabetic patients aged 15-50 years". Diabet Med. 7 (5): 438–44. doi:10.1111/j.1464-5491.1990.tb01420.x. PMID 2142042.
- ↑ Ebenezer GJ, O'Donnell R, Hauer P, Cimino NP, McArthur JC, Polydefkis M (2011). "Impaired neurovascular repair in subjects with diabetes following experimental intracutaneous axotomy". Brain. 134 (Pt 6): 1853–63. doi:10.1093/brain/awr086. PMC 3140859. PMID 21616974.
- ↑ Mayfield JA, Reiber GE, Sanders LJ, Janisse D, Pogach LM (1998). "Preventive foot care in people with diabetes". Diabetes Care. 21 (12): 2161–77. doi:10.2337/diacare.21.12.2161. PMID 9839111.
- ↑ LoGerfo FW, Coffman JD (1984). "Current concepts. Vascular and microvascular disease of the foot in diabetes. Implications for foot care". N Engl J Med. 311 (25): 1615–9. doi:10.1056/NEJM198412203112506. PMID 6390204.
- ↑ Venermo M, Vikatmaa P, Terasaki H, Sugano N (2012). "Vascular laboratory for critical limb ischaemia". Scand J Surg. 101 (2): 86–93. doi:10.1177/145749691210100203. PMID 22623440.
- ↑ McMillan DE (1985). "Blood flow and the localization of atherosclerotic plaques". Stroke. 16 (4): 582–7. doi:10.1161/01.str.16.4.582. PMID 2411027.
- ↑ 10.0 10.1 10.2 Alexiadou K, Doupis J (2012). "Management of diabetic foot ulcers". Diabetes Ther. 3 (1): 4. doi:10.1007/s13300-012-0004-9. PMID 22529027.
- ↑ Noor S, Zubair M, Ahmad J (2015). "Diabetic foot ulcer--A review on pathophysiology, classification and microbial etiology". Diabetes Metab Syndr. 9 (3): 192–9. doi:10.1016/j.dsx.2015.04.007. PMID 25982677.
- ↑ Semenza GL (2012). "Hypoxia-inducible factors in physiology and medicine". Cell. 148 (3): 399–408. doi:10.1016/j.cell.2012.01.021. PMC 3437543. PMID 22304911.
- ↑ Semenza GL (2014). "Oxygen sensing, hypoxia-inducible factors, and disease pathophysiology". Annu Rev Pathol. 9: 47–71. doi:10.1146/annurev-pathol-012513-104720. PMID 23937437.
- ↑ Catrina SB, Zheng X (2016). "Disturbed hypoxic responses as a pathogenic mechanism of diabetic foot ulcers". Diabetes Metab Res Rev. 32 Suppl 1: 179–85. doi:10.1002/dmrr.2742. PMID 26453314.
- ↑ Botusan IR, Sunkari VG, Savu O, Catrina AI, Grünler J, Lindberg S; et al. (2008). "Stabilization of HIF-1alpha is critical to improve wound healing in diabetic mice". Proc Natl Acad Sci U S A. 105 (49): 19426–31. doi:10.1073/pnas.0805230105. PMC 2614777. PMID 19057015.
- ↑ Mace KA, Yu DH, Paydar KZ, Boudreau N, Young DM (2007). "Sustained expression of Hif-1alpha in the diabetic environment promotes angiogenesis and cutaneous wound repair". Wound Repair Regen. 15 (5): 636–45. doi:10.1111/j.1524-475X.2007.00278.x. PMID 17971009.
- ↑ Catrina SB, Okamoto K, Pereira T, Brismar K, Poellinger L (2004). "Hyperglycemia regulates hypoxia-inducible factor-1alpha protein stability and function". Diabetes. 53 (12): 3226–32. doi:10.2337/diabetes.53.12.3226. PMID 15561954.
- ↑ Bento CF, Fernandes R, Ramalho J, Marques C, Shang F, Taylor A; et al. (2010). "The chaperone-dependent ubiquitin ligase CHIP targets HIF-1α for degradation in the presence of methylglyoxal". PLoS One. 5 (11): e15062. doi:10.1371/journal.pone.0015062. PMC 2993942. PMID 21124777.
- ↑ Jhamb S, Vangaveti VN, Malabu UH (2016). "Genetic and molecular basis of diabetic foot ulcers: Clinical review". J Tissue Viability. 25 (4): 229–236. doi:10.1016/j.jtv.2016.06.005. PMID 27372176.
- ↑ Rafehi H, El-Osta A, Karagiannis TC (2011). "Genetic and epigenetic events in diabetic wound healing". Int Wound J. 8 (1): 12–21. doi:10.1111/j.1742-481X.2010.00745.x. PMID 21159125.
- ↑ Laato M, Kähäri VM, Niinikoski J, Vuorio E (1987). "Epidermal growth factor increases collagen production in granulation tissue by stimulation of fibroblast proliferation and not by activation of procollagen genes". Biochem J. 247 (2): 385–8. doi:10.1042/bj2470385. PMC 1148420. PMID 3501286.
- ↑ Singh K, Singh VK, Agrawal NK, Gupta SK, Singh K (2013). "Association of Toll-like receptor 4 polymorphisms with diabetic foot ulcers and application of artificial neural network in DFU risk assessment in type 2 diabetes patients". Biomed Res Int. 2013: 318686. doi:10.1155/2013/318686. PMC 3725976. PMID 23936790.