Variant generator algorithm deals with SPECIALIST lexicon .Acronyms, abbreviations and synonyms of the generator are computed taking into consideration the computation of the derivational variants and its synonyms. The synonyms of the acronyms and abbreviation set are calculated. Finally the acronyms and abbreviation for the synonym set are calculated. Melathesaurus Candidates For each noun phrase, there are metathesaurus candidates that consist of at least one variant provided -by variant generator. Metamap uses word index to detect the metathesaurus candidates Moreover, it purposes the preferred term if a string doesn't found exactly in word index. Candidates are ranked upon the computation of the evaluation function. Evaluation Function: A weight score is calculated for every mapped metathesaurus candidate and noun phrase. Evaluation function [22] is the average of four metrics that reflect the strength of the mapping. The range of the evaluation function starts from 0 up to 1000. The higher score indicates strong match. Centrality determines if the mapped source is a head of a phrase. Variation metric is applied to determine the distance between the mapped term and the root of the word source. Coverage and cohesiveness metrics are applied to show the appropriateness of matching between the source word and candidate UMLS.