Best range of UV light used for treatment of skin diseases:

Ans. b (200 to 400 nm) (Ref. Robbins, Pathologic basis of disease, 7th/pg.321, Table 9-19)PUVA (Psoralen Ultra Voilet A) therapy has gratifying results in treatment of severe psoriasis and the range of UV light used is 200-400 nm. Initial LesionsLocation of Initial LesionsOther FindingsDiagnostic AidsTreatmentPsoriasisPink-red, silvery scale, sharply demarcatedElbows, knees, scalp, presacral areaNail dystrophy, arthritis, pustulesSkin biopsyTopical glucocorticoids, vitamin D; UV-B (narrowband); oral retinoid and/or PUVA; MTX, cyclosporine, anti-TNF agentsULTRAVIOLET RAYS# There is ample evidence from epidemiologic studies that UV rays derived from the sun induce an increased incidence of squamous cell carcinoma, BCC, and possibly malignant melanoma of the skin.# The UV portion of the solar spectrum can be divided into three wavelength ranges:- UVA (320 to 400 nm),- UVB (280 to 320 nm), and- UVC (200 to 280 nm).# UVB is believed to be responsible for the induction of cutaneous cancers.# UVC, although a potent mutagen, is not considered significant because it is filtered out by the ozone shield around the earth (hence the concern about ozone depletion).# UV rays have a number of effects on cells, including inhibition of cell division, inactivation of enzymes induction of mutations and, in sufficient dosage, death of cells.# The carcinogenicity of UVB light is attributed to its formation of pyrimidine dimers in DNA.# This type of DNA damage is repaired by the nucleotide excision repair (NER) pathway.# There are five steps in NER:- Recognition of the DNA lesion,- Incision of the damaged strand on both sites of the lesion,- Removal of the damaged nucleotide,- Synthesis of a nucleotide patch, and- Its ligation.# The importance of the NER pathway of DNA repair is most graphically illustrated by a study of patients with the hereditary disorder xeroderma pigmentosum. This autosomal recessive disorder is characterized by extreme photo- sensitivity, a 2000-fold increased risk of skin cancer in sun-exposed skin and, in some cases, neurologic abnormalities.