An overgrowth syndrome with a wide spectrum of abnormalities, including gigantism of the hands and/or feet, pigmented nevi with variable distribution, hemihypertrophy which may be limited to face, ears, shoulder girdle, thorax, and arms or involve the entire side of the body. Hypertrophic changes are generally associated with subcutaneous hamartomas, skull defects, occasional cardiomyopathy, early growth acceleration, and cystiform pulmonary abnormalities. The complete phenotype of this syndrome often evolves over a period of time, hence the name which denotes its polymorphous character. Named after Proteus, a Greek god who could change his shape at will. A localized form is referred to as the Fishman syndrome.