Causes / typical injury mechanism: Macrodactyly (localized gigantism) is a nonhereditary condition that causes congenital enlargement of the digits of the hands and occasionally the feet.

Classic history and presentation: Macrodactyly is most commonly seen in the hands, with 95% of cases being unilateral. It most often involves the preaxial side of the hand or foot. The most common distribution is along the median nerve or the digital nerve distribution.

Although this condition is most often isolated, it may be seen in conjunction with vascular malformations (eg, hemangiomas, lymphangiomatosis), Proteus syndrome, neurofibromatosis, Klippel-Trenaunay syndrome, Maffucci syndrome, tuberous sclerosis, and multiple enchondromatosis.

Prevalence:

• Age – Generally presents at birth but can progress.
• Sex / gender – More common in boys than in girls.

Pathophysiology: The pathophysiology is uncertain; however, there are a few hypotheses.

• There is increased proliferation of fibroblasts and/or osteoblasts between the periosteum and cortical bone. This increased proliferation of cells could then cause increased phalangeal growth.
• A dysregulation caused by a postzygotic gain in function mutation in PIK3CA, which is part of the mTOR pathway.

Grade / classification system:
Type 1: Macrodactyly with nerve-oriented lipofibromatosis

• Static subtype – The proportion of enlargement remains constant throughout growth.
• Progressive subtype – The proportion of enlargement increases with age.

Type 2: Macrodactyly with neurofibromatosis
Type 3: Macrodactyly with hyperostosis
Type 4: Macrodactyly with hemihypertrophy