The most common association with coarse pitting of nails and onycholysis is-

In psoriasis the nail changes are pitting, nail plate thickening, subungual hyperkeratosis, discoloration and dystrophy of nail plate, onycholysis and oil spots. Psoriasis is a chronic dermatosis characterized by an unpredictable course of remission and relapse and presence at typical sites of well defined, erythematous papules and plaques , which are surmounted with large , loose silvery scales . There is frequent nail and joint involvement. skin lesions -erythematous papules and plaques, silvery white scales, grattage sign positive-appearence like candle wax, inflammatory ring of woronoff at the advancing edge hypopigmentaion at the edge of lesion, membrane of burkley- moist red membrane seen after scraping of scales. auspitz sign positive- pinpoint bleeding points after scraping of lesion .this is due to supra papillary thinning and capillary dilatation koebners phenomenon is present. sites of predilection- extensors, dorsum of hands and feet,elbows knees, buttocks,lower back, scalp nails in psoriasis- coarse pitting, onycholysis,subungual hyperkeratosis, yellowish discolouration,splinter hemorrhages. coarse pitting with onycholysis if nails in association with well defined scaly plaques characteristic of psoriasis. polygonal papules and violaceous papules are seen in lichen planus . nail changes seen are fine pitting. IADVL textbook of dermatology,page 1036.