37 Macrodactyly

10.1055/b-0038-162689

37 Macrodactyly

Carolyn M. Pike and Brian I. Labow

Summary

Macrodactyly is a rare congenital overgrowth disorder of the upper or lower limb. Although all tissue types are affected variably, proportion and patterning are maintained within the affected territory, and structures appear grossly normal. The disease process often follows a sensory nerve distribution within the hand or foot. Recent genetic studies have identified somatic mosaic gain-of-function mutations in the kinase PIK3CA in patients with macrodactyly, as well as a number of related overgrowth conditions. However, the basis for phenotypic variation, such as severity and tissue distribution of overgrowth, as well as rate of growth, remains to be established. The diagnosis of macrodactyly should be reserved for patients with a sporadic, isolated congenital digital enlargement affecting all tissue types not attributable to a syndrome or underlying vascular anomaly. Current treatment options are limited to surgery and can include staged debulking of soft tissue, epiphysiodesis, osteotomy, or ray amputation. Longitudinal growth is far easier to correct than circumferential growth. The major goals of treatment are to enable optimal hand function and to provide an aesthetic limb. Minor complications of operative treatment include hypertrophic scarring, decreased sensation, and flexion contractures. As patients age, many will develop progressive stiffness in the affected digit, and some will show radiological signs of a progressive osteoarthritis. In the future, pharmacotherapy may provide an additional treatment option for patients with digital overgrowth.

37.1 Introduction

Macrodactyly is a rare congenital overgrowth disorder affecting the digits of the upper or lower extremity. The condition accounts for 0.9% of all upper limb congenital anomalies. Macrodactyly is sporadic, nonsyndromic, and often follows a sensory nerve distribution within the hand or foot. Overgrowth is usually noted at birth; however, both the extent and rate of growth can vary widely. Macrodactyly can be classified by rate of growth, with the term “progressive” describing rapid, disproportionate enlargement relative to the rest of the limb, while “static” refers to a slower, proportionate growth. Although all tissue types are affected variably, proportion and patterning are maintained within the affected territory, and structures appear grossly normal. Another means of classification has been through the predominant tissue type involved, for example, lipomatous macrodactyly for cases with gross excess of adipose tissue out of proportion to other tissue types. In contrast, nerve-territory-oriented macrodactyly has been used for digits with enlarged nerves within the affected zone of overgrowth that clearly follow a sensory nerve territory. A biological distinction between these two clinical entities has not been shown. To further confound the situation, a wide array of descriptive terms and eponyms has also been used to refer to macrodactyly. Given the rarity of this condition, the lack of precision in nomenclature, and our limited understanding of the pathophysiology of this disorder, it is not surprising that there exists a paucity of literature on treatment options and long-term outcomes.

37.2 Diagnosis

In most cases, digital enlargement is obvious soon after birth. Occasionally, minor degrees of enlargement may not be detected until later in infancy, when continued enlargement occurs (Fig. 37‑1, Fig. 37‑2). A variety of syndromic and nonsyndromic causes for digital enlargement exist. A thorough physical examination to look for other findings or a local or regional cause for the overgrowth (e.g., expansile mass, vascular anomaly) should be carefully undertaken. The diagnosis of macrodactyly should be reserved for patients with a sporadic, isolated congenital digital enlargement affecting all tissue types not attributable to a syndrome or underlying vascular anomaly. Radiographic imaging such as ultrasonography or plain films can be useful to document the absence of a vascular lesion and the presence of skeletal involvement, respectively. Magnetic resonance imaging can also be used to plan debulking procedures by documenting the extent of fatty overgrowth in the limb that frequently contributes to additional limb or digit girth and weight. Recent genetic studies have identified somatic mosaic gain-of-function mutations in the kinase PIK3CA in patients with macrodactyly. These mutations have been implicated in a growing number of related overgrowth conditions as well. However, the basis for phenotypic variation, such as severity and tissue distribution of overgrowth, as well as rate of growth, remains to be established.