World Library  
Flag as Inappropriate
Email this Article
 

Lichen planus

Lichen planus
Lichen planus affecting the shins.
Classification and external resources
Specialty Dermatology
ICD-10 L43
ICD-9-CM 697.0
DiseasesDB 7452
MedlinePlus 000867
eMedicine derm/233 derm/663
MeSH D008010, D017676

Lichen planus (LP) is a disease of the skin and/or mucous membranes that resembles lichen. The cause is unknown, but it is thought to be the result of an autoimmune process with an unknown initial trigger. There is no cure, but many different medications and procedures have been used to control the symptoms.

The term lichenoid reaction (or lichenoid lesion) refers to a lesion of similar or identical histopathologic and clinical appearance to lichen planus (i.e. an area which looks the same as lichen planus, both to the naked eye and under a microscope).[1][2] Sometimes dental materials or certain medications can cause a lichenoid reaction.[1] They can also occur in association with graft versus host disease.[1][3]:258

Contents

  • Classification 1
    • Site 1.1
    • Pattern 1.2
    • Overlap syndromes 1.3
  • Signs and symptoms 2
    • Cutaneous lichen planus 2.1
    • Mucosal lichen planus 2.2
      • Oral lichen planus 2.2.1
  • Causes 3
  • Diagnosis 4
    • Histopathology 4.1
    • Differential diagnosis 4.2
  • Treatment 5
    • Cutaneous lichen planus 5.1
    • Oral lichen planus 5.2
  • Prognosis 6
  • Epidemiology 7
  • History 8
  • Notes 9
  • References 10
  • External links 11

Classification

Lichen planus has been described as an autoimmune disease,[4] a dermatosis,[5] a papulosquamous disorder, a mucocutaneous disease,[6] and an inflammatory disease.[7]

Lichen planus lesions are so called because of their "lichen-like" appearance[8] and can be classified by the site they involve, or by their morphology.

Site

Lichen planus may be categorized as affecting mucosal or cutaneous surfaces.

  • Cutaneous forms are those affecting the skin, scalp, and nails.[5][6][9]
  • Mucosal forms are those affecting the lining of the gastrointestinal tract (mouth, pharynx, esophagus, stomach, anus), larynx, and other mucosal surfaces including the genitals, peritoneum, ears, nose, bladder and conjunctiva of the eyes.[7][10][11]

Pattern

Lichen planus lesions can occur in many different forms:

Lesion morphology Description[12][13]
Annular 'Ring-shaped' lesions that develop gradually from single small pigmented spots into circular groups of papules with clear, unaffected skin in the center. Annular lesions occur in approximately ten percent of lichen planus cases. The ring-like lesions may very slowly enlarge, co-join and morph into larger irregular (serpentine) bands, sometimes accompanied by lines (See Linear, below).
Linear Papules are arranged in a line (the "Blaschko line").[14] This pattern may develop secondary to trauma (koebnerization) or, uncommonly, as a spontaneous, isolated eruption, usually on the extremities, and rarely on the face.[15]
Hypertrophic This pattern usually occurs on the extremities, especially the shins and the interphalangeal joints, and tends to be the most pruritic variant of lichen planus. Also known as "Lichen planus verrucosus".
Atrophic This morphology is characterized by the presence of a few well-demarcated, white-bluish papules or plaques with central superficial atrophy. This is a rare variant of lichen planus.
Bullous This morphology is characterized by the development of vesicles and bullae with the skin lesions. This is a rare variant of lichen planus, and also known as "Vesiculobullous lichen planus".
Ulcerative This morphology is characterized by chronic, painful bullae and ulceration of the feet, often with cicatricial sequelae evident. This is a rare variant of lichen planus.
Pigmented This morphology is characterized by hyperpigmented, dark-brown macules in sun-exposed areas and flexural folds. This is a rare variant of lichen planus.

Overlap syndromes

Occasionally, lichen planus is known to occur with other conditions. For example:

  • Lupus erythematosus overlap syndrome. Lesions of this syndrome share features of both lupus erythematosus and lichen planus. Lesions are usually large and hypopigmented, atrophic, and with a red-to-blue colour and minimal scaling. Telangectasia may be present.[13][16]
  • Lichen sclerosus overlap syndrome, sharing features of lichen planus and lichen sclerosus.[17]

Signs and symptoms

Lichen planus affecting the lower lip.

Although lichen planus can present with a variety of lesions, the most common presentation is as a well-defined area of purple-coloured, itchy, flat-topped papules with interspersed lacy white lines (Wickham's striae). This description is known as the characteristic "6 Ps" of lichen planus: planar (flat-topped), purple, polygonal, pruritic, papules, and plaques.[9] This rash, after regressing, is likely to leave an area of hyperpigmentation that slowly fades. That said, a variety of other lesions can also occur.[8]

Cutaneous lichen planus

Cutaneous lichen planus on the shin.
Lichen planus involving the nails.

Variants of cutaneous lichen planus are distinguished based upon the appearance of the lesions and/or their distribution.[18] Lesions can affect the:

  • Extremities (face, dorsal hands, arms, and nape of neck).[1] This is more common in Middle Eastern countries in spring and summer, where sunlight appears to have a precipitating effect.[15][19][20]
  • Palms and soles
  • Intertriginous areas of the skin. This is also known as "Inverse lichen planus".[15]
  • Nails[21] characterized by irregular longitudinal grooving and ridging of the nail plate, thinning of the nail plate, pterygium formation, shedding of the nail plate with atrophy of the nail bed, subungual keratosis, longitudinal erthronychia (red streaks), and subungual hyperpigmentation.[22] A sand-papered appearance is present in around 10% of individuals with nail lichen planus.[21]
  • Scalp. This is also known as lichen planopilaris, acuminatus, follicular lichen planus, and peripilaris,[23] characterised by violaceous, scaly, pruritic papules. Scalp lichen planus can cause scarring alopecia if it is untreated.[9][20][24]
  • Hair. This variant causes inflammation of hair follicles and gradual replacement with scarring. About 10% of people with lichen planus have the scalp or nail variants of the condition.[9]

Other variants may include:

  • Lichen planus pemphigoides characterized by the development of tense blisters atop lesions of lichen planus or the development vesicles de novo on uninvolved skin.[25]
  • Keratosis lichenoides chronica (also known as "Nekam's disease") is a rare dermatosis characterized by violaceous papular and nodular lesions, often arranged in a linear or reticulate pattern on the dorsal hands and feet, extremities, and buttock, and some cases manifests by sorrheic dermatitis like eruption on the scalp and face, also palmo plantar keratosis has been reported.[15][26][27]
  • Lichenoid keratoses (also known as "Benign lichenoid keratosis," and "Solitary lichen planus"[15]) is a cutaneous condition characterized by brown to red scaling maculopapules, found on sun-exposed skin of extremities.[15][28] Restated, this is a cutaneous condition usually characterized by a solitary dusky-red to violaceous papular skin lesion.[29]
  • Lichenoid dermatitis represents a wide range of cutaneous disorders characterized by lichen planus-like skin lesions.[15][28]

Mucosal lichen planus

Lichen planus on the lips and the lateral border of the tongue

Lichen planus affecting mucosal surfaces may have one lesion or be multifocal.[30] Examples of lichen planus affecting mucosal surfaces include:[30]

  • Esophageal lichen planus, affecting the esophageal mucosa. This can present with difficulty or pain when swallowing due to oesophageal inflammation, or as the development of an esophageal stricture. It has also been hypothesized that it is a precursor to squamous cell carcinoma of the esophagus.[10][31]
  • Genital lichen planus, which may cause lesions on the glans penis or skin of the scrotom in males, and the vulva or vagina in females.[9] Symptoms may include lower urinary tract symptoms associated with stenosis of the urethra, painful sexual intercourse, and itching.[9] In females, Vulvovaginal-gingival syndrome, is severe and distinct variant affecting the vulva, vagina, and gums, with complications including scarring, vaginal stricture formation,[32] or vulva destruction.[33] The corresponding syndrome in males, affecting the glans penis and gums, is the peno-gingival syndrome.[15] It is associated with HLA-DQB1.[15][34]

Oral lichen planus

Oral lichen planus (also termed oral mucosal lichen planus),[35] is a form of mucosal lichen planus, where lichen planus involves the oral mucosa, the lining of the mouth. This may occur in combination with other variants of lichen planus.[36] Six clinical forms of oral lichen planus are recognized:[36]

  • Reticular, the most common presentation of oral lichen planus,[4] is characterised by the net-like or spider web-like appearance of lacy white lines, oral variants of Wickham's straiae.[36] This is usually asymptomatic.[4]
  • Erosive/ulcerative, the second most common form of oral lichen planus,[4] is characterised by oral ulcers presenting with persistent, irregular areas of redness, ulcerations and erosions covered with a yellow slough. This can occur in one or more areas of the mouth. In 25% of people with erosive oral lichen planus, the gums are involved, described as desquamative gingivitis (a condition not unique to lichen planus). This may be the initial or only sign of the condition.[36]
  • Papular, with white papules.
  • Plaque-like appearing as a white patch which may resemble leukoplakia.[36]
  • Atrophic, appearing as areas. Atrophic oral lichen planus may also manifest as desquamative gingivitis.[36]
  • Bullous, appearing as fluid-filled vesicles which project from the surface.

These types often coexist in the same individual. Oral lichen planus tends to present bilaterally as mostly white lesions on the inner cheek,[4] although any mucosal site in the mouth may be involved. Other sites, in decreasing order of frequency, may include the tongue, lips, gingivae, floor of the mouth, and very rarely, the palate.[4]

Generally, oral lichen planus tends not to cause any discomfort or pain, although some people may experience soreness when eating or drinking acidic or spicy foodstuffs or beverages.[36] When symptoms arise, they are most commonly associated with the atrophic and ulcerative subtypes. These symptoms can include a burning sensation to severe pain.[4]

Causes

The cause of lichen planus is unknown,[8][34][37] but it is not contagious and does not involve any known pathogen.[38] It is thought to be a T cell mediated autoimmune reaction (where the body's immune system targets its own tissues).[4] This autoimmune process triggers apoptosis of the epithelial cells.[4] Several cytokines are involved in lichen planus, including tumor necrosis factor alpha, interferon gamma, interleukin-1 alpha, interleukin 6, and interleukin 8.[4] This autoimmune, T cell mediated, process is thought to be in response to some antigenic change in the oral mucosa, but a specific antigen has not been identified.[4]

Where a causal or triggering agent is identified, this is termed a lichenoid reaction rather than lichen planus. These may include:[11]

It has been suggested that lichen planus may respond to stress, where lesions may present during times of stress. Lichen planus can be part of Grinspan's syndrome.

It has also been suggested that mercury exposure may contribute to lichen planus.[40]

Diagnosis

Lichen planus lesions are diagnosed clinically by their "lichen-like" appearance.[8] A biopsy can be used to rule out conditions that may resemble lichen planus, and can pick up any secondary malignancies.[41]

Histopathology

Micrograph of lichen planus. H&E stain.

Lichen planus has a unique microscopic appearance that is similar between cutaneous, mucosal and oral. A Periodic acid-Schiff stain of the biopsy may be used to visualise the specimen. Histological features seen include:[42]

  • thickening of the stratum corneum both with nuclei present (parakeratosis) and without (orthokeratosis). Parakeratosis is more common in oral variants of lichen planus.
  • thickening of the stratum granulosum
  • thickening of the stratum spinosum (acanthosis) with formation of colloid bodies (also known as Civatte bodies, Sabouraud bodies) that may stretch down to the lamina propria.
  • liquefactive degeneration of the stratum basale, with separation from the underlying lamina propria, as a result of desmosome loss, creating small spaces (Max Joseph spaces).
  • Infiltration of T cells in a band-like pattern into the dermis[4] "hugging" the basal layer.
  • Development of a "saw-tooth" appearance of the rete pegs, which is much more common in non-oral forms of lichen planus.

Differential diagnosis

The differential diagnosis for OLP includes:

Treatment

There is no cure for lichen planus,[4] and so treatment of cutaneous and oral lichen planus is for symptomatic relief or due to cosmetic concerns.[4][8][41] When medical treatment is pursued, first-line treatment typically involves corticosteroids,[8] and removal of any triggers.[39] Without treatment, most lesions will spontaneously resolve within 6–9 months for cutaneous lesions,[8] and longer for mucosal lesions [42]

Cutaneous lichen planus

Many different treatments have been reported for cutaneous lichen planus, however there is a general lack of evidence of efficacy for any treatment.[14][44] Treatments tend to be prolonged, partially effective and disappointing.[14] First-line treatments may include retinoids such as Acitretin, or corticosteroids [8][14][44]

A variety of other therapies are also used if these are unsuccessful. These include oral corticosteroids, vitamin D3 analogues, antibiotics such as Dapsone, hydroxychloroquine and Cyclosporin, some anti-coagulants, and psoralen plus ultraviolet-A.[8][14][44]

Cosmetic treatments may include laser surgery, cryotherapy, and phototherapy.[14][44]

Oral lichen planus

Reassurance that the condition is benign, elimination of precipitating factors and improving oral hygiene are considered initial management for symptomatic OLP, and these measures are reported to be useful.[4] Treatment usually involves topical corticosteroids (such as betamethasone, clobetasol, dexamethasone, and triamcinolone) and analgesics, or if these are ineffective and the condition is severe, the systemic corticosteroids may be used. Calcineurin inhibitors (such as pimecrolimus, tacrolimus) or cyclosporin) are sometimes used.[4]

Prognosis

In contrast to cutaneous lichen planus, lichen planus lesions in the mouth may persist for many years,[41] and tend to be difficult to treat, with relapses being common.[34] Atrophic/erosive lichen planus is associated with a small risk of malignant transformation,[41] and so people with OLP tend to be kept on long term review to detect any potential change early. Sometimes OLP can become secondarily infected with Candida organisms.

Epidemiology

The overall prevalence of lichen planus in the general population is about 0.1 - 4%.[9] It generally occurs more commonly in females, in a ratio of 3:2, and most cases are diagnosed between the ages of 30 and 60, but it can occur at any age.[9][45]

Oral lichen planus is relatively common,[34] It is one of the most common mucosal diseases. The prevalence in the general population is about 1.27-2.0%,[4][41] and it occurs more commonly middle aged people.[4] OLP in children is rare. About 50% of females with oral lichen planus were reported to have undiagnosed vulvar lichen planus.[9]

History

Lichen planus was first reported in 1869 by Erasmus Wilson.[42]

Notes

  1. ^ Cutaneous lichen planus affecting the extremities is also known as "Lichen planus actinicus", "Actinic lichen niditus," "Lichen planus atrophicus annularis," "Lichen planus subtropicus," "Lichen planus tropicus," "Lichenoid melanodermatitis," and "Summertime actinic lichenoid eruption"

References

  1. ^ a b c Greenberg MS, Glick M, Ship JA (2008). Burket's oral medicine (11th ed.). Hamilton, Ont.: BC Decker. pp. 89–97.  
  2. ^ Lewis MAO, Jordan RCK (2012). Oral medicine (2nd ed.). London: Manson Publishing. pp. 66–72.  
  3. ^ Barnes L (editor) (2009). Surgical pathology of the head and neck (3rd ed.). New York: Informa healthcare.  
  4. ^ a b c d e f g h i j k l m n o p q r Thongprasom, K; Carrozzo, M; Furness, S; Lodi, G (Jul 6, 2011). "Interventions for treating oral lichen planus.". The Cochrane database of systematic reviews (7): CD001168.  
  5. ^ a b Asch, S; Goldenberg, G (March 2011). "Systemic treatment of cutaneous lichen planus: an update.". Cutis; cutaneous medicine for the practitioner 87 (3): 129–34.  
  6. ^ a b Sharma, A; Białynicki-Birula, R; Schwartz, RA; Janniger, CK (July 2012). "Lichen planus: an update and review.". Cutis; cutaneous medicine for the practitioner 90 (1): 17–23.  
  7. ^ a b Cheng, S; Kirtschig, G; Cooper, S; Thornhill, M; Leonardi-Bee, J; Murphy, R (Feb 15, 2012). "Interventions for erosive lichen planus affecting mucosal sites.". The Cochrane database of systematic reviews 2: CD008092.  
  8. ^ a b c d e f g h i Limited, Therapeutic Guidelines (2009). Therapeutic guidelines. (Version 3. ed.). North Melbourne, Vic.: Therapeutic Guidelines. pp. 254–255, 302.  
  9. ^ a b c d e f g h i Usatine, RP; Tinitigan, M (Jul 1, 2011). "Diagnosis and treatment of lichen planus". American family physician 84 (1): 53–60.  
  10. ^ a b Yamada T, Alpers DH; et al. (2009). Textbook of gastroenterology (5th ed.). Chichester, West Sussex: Blackwell Pub. p. 3304.  
  11. ^ a b Treister NS, Bruch JM (2010). Clinical oral medicine and pathology. New York: Humana Press. pp. 59–62.  
  12. ^ Freedberg, Irwin M., ed. (2003). Fitzpatrick's dermatology in general medicine (6th ed.). New York, NY: McGraw-Hill. pp. 465–8.  
  13. ^ a b James, William D.; Elston, Dirk M.; Berger, Timothy G. Andrews' Diseases of the skin : clinical dermatology (11th ed.). London: Saunders/ Elsevier. pp. 219–24.  
  14. ^ a b c d e f Gorouhi, F; Firooz A; Khatami A; Ladoyanni E; Bouzari N; Kamangar F; Gill JK (2009). "Interventions for cutaneous lichen planus". Cochrane Database of Systematic Reviews (4).  
  15. ^ a b c d e f g h i Bolognia, Jean L.; Jorizzo, Joseph L.; Rapini, Ronald P., eds. (2008). Dermatology (2nd ed.). St. Louis: Mosby/Elsevier.  
  16. ^ Freedberg, Irwin M., ed. (2003). Fitzpatrick's dermatology in general medicine (6th ed.). New York, NY: McGraw-Hill. pp. 366, 470–1.  
  17. ^ a b James, William D.; Elston, Dirk M.; Berger, Timothy G. Andrews' Diseases of the skin : clinical dermatology (11th ed.). London: Saunders/ Elsevier. p. 220.  
  18. ^ Freedberg, Irwin M., ed. (2003). Fitzpatrick's dermatology in general medicine (6th ed.). New York, NY: McGraw-Hill. p. 466.  
  19. ^ Freedberg, Irwin M., ed. (2003). Fitzpatrick's dermatology in general medicine (6th ed.). New York, NY: McGraw-Hill. p. 468.  
  20. ^ a b James, William D.; Elston, Dirk M.; Berger, Timothy G. Andrews' Diseases of the skin : clinical dermatology (11th ed.). London: Saunders/ Elsevier. p. 223.  
  21. ^ a b Gordon, KA; Vega, JM; Tosti, A (Nov–Dec 2011). "Trachyonychia: a comprehensive review". Indian journal of dermatology, venereology and leprology 77 (6): 640–5.  
  22. ^ James, William D.; Elston, Dirk M.; Berger, Timothy G. Andrews' Diseases of the skin : clinical dermatology (11th ed.). London: Saunders/ Elsevier. p. 781.  
  23. ^ Freedberg, Irwin M., ed. (2003). Fitzpatrick's dermatology in general medicine (6th ed.). New York, NY: McGraw-Hill. p. 467.  
  24. ^ Cevasco NC, Bergfeld WF, Remzi BK, de Knott HR (2007). "A case-series of 29 patients with lichen planopilaris: the Cleveland Clinic Foundation experience on evaluation, diagnosis, and treatment". J. Am. Acad. Dermatol. 57 (1): 47–53.  
  25. ^ Freedberg, Irwin M., ed. (2003). Fitzpatrick's dermatology in general medicine (6th ed.). New York, NY: McGraw-Hill. p. 471.  
  26. ^ Freedberg, Irwin M., ed. (2003). Fitzpatrick's dermatology in general medicine (6th ed.). New York, NY: McGraw-Hill. p. 472.  
  27. ^ James, William D.; Elston, Dirk M.; Berger, Timothy G. Andrews' Diseases of the skin : clinical dermatology (11th ed.). London: Saunders/ Elsevier. p. 224.  
  28. ^ a b Freedberg, Irwin M., ed. (2003). Fitzpatrick's dermatology in general medicine (6th ed.). New York, NY: McGraw-Hill. p. 473.  
  29. ^ James, William D.; Elston, Dirk M.; Berger, Timothy G. Andrews' Diseases of the skin : clinical dermatology (11th ed.). London: Saunders/ Elsevier. p. 639.  
  30. ^ a b Ebrahimi, M; Lundqvist, L; Wahlin, YB; Nylander, E (October 2012). "Mucosal lichen planus, a systemic disease requiring multidisciplinary care: a cross-sectional clinical review from a multidisciplinary perspective". Journal of lower genital tract disease 16 (4): 377–80.  
  31. ^ Chandan, VS; Murray, JA; Abraham, SC (June 2008). "Esophageal lichen planus". Archives of pathology & laboratory medicine 132 (6): 1026–9.  
  32. ^ Panagiotopoulou, N; Wong, CS; Winter-Roach, B (April 2010). "Vulvovaginal-gingival syndrome.". Journal of obstetrics and gynaecology : the journal of the Institute of Obstetrics and Gynaecology 30 (3): 226–30.  
  33. ^ Schlosser, BJ (May–Jun 2010). "Lichen planus and lichenoid reactions of the oral mucosa.". Dermatologic therapy 23 (3): 251–67.  
  34. ^ a b c d Nico, MM; Fernandes, JD; Lourenço, SV (Jul–Aug 2011). "Oral lichen planus.". Anais brasileiros de dermatologia 86 (4): 633–41; quiz 642–3.  
  35. ^ Alam, F; Hamburger, J (May 2001). "Oral mucosal lichen planus in children.". International journal of paediatric dentistry / the British Paedodontic Society [and] the International Association of Dentistry for Children 11 (3): 209–14.  
  36. ^ a b c d e f g Scully C (2008). Oral and maxillofacial medicine : the basis of diagnosis and treatment (3rd ed.). Edinburgh: Churchill Livingstone. pp. 192–199.  
  37. ^ Roopashree, MR; Gondhalekar, RV; Shashikanth, MC; George, J; Thippeswamy, SH; Shukla, A (November 2010). "Pathogenesis of oral lichen planus--a review.". Journal of oral pathology & medicine : official publication of the International Association of Oral Pathologists and the American Academy of Oral Pathology 39 (10): 729–34.  
  38. ^ a b c d Davidson's principles and practice of medicine. (21st ed.). Edinburgh: Churchill Livingstone/Elsevier. 2010. pp. 1265–1266.  
  39. ^ a b Issa, Y; Brunton, PA; Glenny, AM; Duxbury, AJ (November 2004). "Healing of oral lichenoid lesions after replacing amalgam restorations: a systematic review.". Oral surgery, oral medicine, oral pathology, oral radiology, and endodontics 98 (5): 553–65.  
  40. ^ Dunsche A, Frank MP, Lüttges J, et al. (April 2003). "Lichenoid reactions of murine mucosa associated with amalgam". The British Journal of Dermatology 148 (4): 741–8.  
  41. ^ a b c d e Kerawala C, Newlands C, ed. (2010). Oral and maxillofacial surgery. Oxford: Oxford University Press. pp. 412–413.  
  42. ^ a b c Scully, C.; El-Kom, M. (1 July 1985). "Lichen planus: review and update on pathogenesis". Journal of Oral Pathology and Medicine 14 (6): 431–458.  
  43. ^ Odell EW (Editor) (2010). Clinical problem solving in dentistry (3rd ed.). Edinburgh: Churchill Livingstone. pp. 159–162, 192.  
  44. ^ a b c d Cribier, B; Frances, C; Chosidow, O (December 1998). "Treatment of lichen planus. An evidence-based medicine analysis of efficacy.". Archives of dermatology 134 (12): 1521–30.  
  45. ^ Yu TC, Kelly SC, Weinberg JM, Scheinfeld NS (March 2003). "Isolated lichen planus of the lower lip". Cutis 71 (3): 210–2.  

External links

  • Lichen planus at DMOZ
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 


Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.