Hyperplasia is a common preneoplastic response to stimulus.[6] Microscopically, cells resemble normal cells but are increased in numbers. Sometimes cells may also be increased in size (hypertrophy).[7] Hyperplasia is different from hypertrophy in that theadaptive cell change in hypertrophy is an increase in thesize of cells, whereas hyperplasia involves an increase in thenumber of cells.[8]
-plasia and -trophy
Anaplasia (structural differentiation loss within a cell or group of cells).
Hyperplasia may be due to any number of causes, including proliferation of basal layer of epidermis to compensate skin loss,chronic inflammatory response,hormonal dysfunctions, orcompensation fordamage ordisease elsewhere.[9] Hyperplasia may be harmless and occur on a particular tissue. An example of a normal hyperplastic response would be the growth and multiplication of milk-secretingglandular cells in thebreast as a response topregnancy, thus preparing for futurebreast feeding.[10]
Perhaps the most interesting and potent[editorializing] effectinsulin-like growth factor 1 (IGF) has on the human body is its ability to cause hyperplasia, which is an actual splitting of cells.[11] By contrast,hypertrophy is what occurs, for example, to skeletal muscle cells duringweight training and is simply an increase in the size of the cells.[12] With IGF use, one is able to cause hyperplasia which actually increases the number of muscle cells present in the tissue.[13] Weight training enables these new cells to mature in size and strength. It is theorized that hyperplasia may also be induced through specific power output training for athletic performance, thus increasing the number of muscle fibers instead of increasing the size of a single fiber.[14]
Hyperplasia is considered to be aphysiological (normal) response to a specific stimulus, and the cells of a hyperplastic growth remain subject to normalregulatory control mechanisms.[5] However, hyperplasia can also occur as apathological response, if an excess of hormone or growth factor is responsible for the stimuli. Similarly to physiological hyperplasia, cells that undergo pathologic hyperplasia are controlled bygrowth hormones, and cease to proliferate if such stimuli are removed.[15] This differs fromneoplasia (the process underlyingcancer and benign tumors), in whichgenetically abnormal cells manage toproliferate in a non-physiological manner which is unresponsive to normal stimuli.[16] That being said, the effects caused by pathologic hyperplasia can provide a suitable foundation from which neoplastic cells may develop.[15]
Hyperplasia of certain tissues may cause disease. Pathologic hyperplasia in these tissues may occur due to infection, physiological stress or trauma, or abnormal levels of particular hormones, such as estrogen, ACTH, or cortisol.[17]
Endometrial hyperplasia – Hyperproliferation of the endometrium, usually in response to unopposedestrogen stimulation in the setting ofpolycystic ovary syndrome or exogenous administration of hormones. Atypical endometrial hyperplasia may represent an earlyneoplastic process which can lead toendometrial adenocarcinoma.[20] The development of endometrial adenocarcinoma from endometrial hyperplasia is a typical example of how the effects of pathologic hyperplasia can lead to neoplasia, and females who exhibit hyperplasia of the endometrium are indeed more likely to develop cancer of these cells.[15]
Patient with hemihyperplasia involving the upper and lower left extremities. Theleg length discrepancy can be noted by the pelvic tilt.
Hemihyperplasia – When only half (or one side) of the body is affected, sometimes generating limbs of different lengths.[21]
Intimal hyperplasia – The thickening of thetunica intima of a blood vessel as a complication of a reconstruction procedure orendarterectomy. Intimal hyperplasia is the universal response of a vessel to injury and is an important reason of late bypass graft failure, particularly in vein and synthetic vascular grafts.[22]
Focal epithelial hyperplasia (also known as Heck's disease) – This is a wart-like growth in the mucous tissues of the mouth or, rarely, throat that is caused by certain sub-types of thehuman papillomavirus (HPV). Heck's disease has not been known to cause cancer.[23]
Myofibre hyperplasia (also known asdouble-muscling) – seen in cattle, genetic mutations cause large muscles due to increased proliferation of myofibres and decreased adipose tissue.[24]
Sebaceous hyperplasia – In this condition, small yellowish growths develop on the skin, usually on the face. This condition is neither contagious nor dangerous.[25]
Compensatoryliver hyperplasia – The liver undergoes cellular division after acute injury, resulting in new cells that restore liver function back to baseline. Approximately 75% of the liver can be acutely damaged or resected with seemingly full regeneration throughhepatocyte division, i.e., hyperplasia. This is what makes living-donor liver transplants possible.[26]
^ab"Prostate Enlargement (Benign Prostatic Hyperplasia)".National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). U.S. Department of Health and Human Services National Institutes of Health. Retrieved2015-05-30.
^"Hyperplasia".MedlinePlus Medical Encyclopedia. National Library of Medicine, U.S. Department of Health and Human Services National Institutes of Health. Retrieved2015-05-30.
^"Cushing disease".MedlinePlus Medical Encyclopedia. National Library of Medicine, U.S. Department of Health and Human Services National Institutes of Health. Retrieved2015-05-30.
^"Congenital adrenal hyperplasia".MedlinePlus Medical Encyclopedia. National Library of Medicine, U.S. Department of Health and Human Services National Institutes of Health. Retrieved2015-05-30.
^"Endometrial Hyperplasia".American College of Obstetricians and Gynecologists (ACOG). Retrieved2015-05-30.
^"Hemihyperplasia - Glossary Entry".Genetics Home Reference. National Library of Medicine, U.S. Department of Health and Human Services. Retrieved2015-05-30.
