Ans A (autoimmune) Ref IADVL text book of Dermatology P1022, Harrisons 17th ed pg 315,It is a T cell mediated autoimmune chronic inflammatory disease.The evidence implicating a key role for an immune pathogenesis relates to:*the association with certain HLA groups (HLA Cw6)*the success of certain immunosuppressive drugs (such as cyclosporin) in improving the clinical state of the disease*reports of the development of psoriasis in recipients of bone marrow transplants from donors with a history of psoriasis.Over 50% of patients with psoriasis report a positive family history.Psoriatic lesions demonstrate infiltrates of activated T cells that are thought to elaborate cytokines responsible for keratinocyte hyperproliferation, which results in the characteristic clinical findings.The etiology of psoriasis is still poorly understood, but there is clearly a genetic component to the disease.Type I (Heriditary)Strong HLA association (HLA CW6)Severe course and early onset, arthropathy more common.Type IISporadicHLA unrelatedMild course and late onsetThe number of cycling cells are increased 7 fold in psoriasis. There is no shortening of the cell cycle.The most important locus for psoriasis susceptibility is Psors 1 (psoriasis susceptibility locus on chr 6p 21.3.T cells(helper) are fundamental in activating the disease process.The trigger to their activation may be conventional antigens or bacterial superantigens.Clinical features of psoriasis-imp featuresMost common clinical type is chronic plaque type.Salmon coloured papules and plaques with silvery scales.Auspitz sign- multiple bleeding points on scraping of psoriatic plaques.Candle sign- charecteristic coherence of scales in psoriasis causes a feeling as if scraping on a candle.The halo ring ofworonoff- around the psoriaric plaque due to deficiency of pgE2.Annulus migrans-mucus membrane lesion in psoriasis.Most common nail change is pitting.Pustular psoriasis- most severe type is von-zumbushtype of generalized pustular psoriasis. It gets precipitated by treatment with irritants& sudden withdrawal of corticosteroids.Skin gets studded with minute sterile pustules which later may fuse to form lakes of pus.Histopathology of psoriasisParakeratosisMicro munro abscess- collection of neutrophils in stratum comeumSpongiform pustules of kogoj- aggregates of neutrophil in stratum spinosum.Acanthosis with regular elongation of rete ridges- camel foot appearance.Edema of dermal papillae with dilated& tortuous capillaries.Treatment of choice for generalized pustular psoriasis & psoriatic erythroderma is-AcetretinBiological therapy of psoriasisDirected at selected targets integral to the pathogenesis of psoriasis.The hyperproliferation seen in psoriasis is due to activated T cells & their cytokines. Biological agents are also used in rheumatoid arthritis, crohn's disease.T cell targetingAlefacept,Efalizumab,Daclizumab,BasiliximabCytokine blockersInfliximab, EtanerceptEtanercept-Human dimenc fusion protein -Anti TNF agentInfliximab-Chimeric monoclonal antibody.For further explanation refer PG HUNT p183, 2008 skin, 2005 Q258