Isolated hemihyperplasia

Isolated hemihyperplasia (IH), also known as isolated hemihypertrophy, is a rare congenital condition characterized by asymmetric overgrowth of one or more body regions, including limbs, the face, or the trunk, without the presence of other syndromic features. The overgrowth may involve bones, soft tissues, organs, or a combination of these structures, and can affect one entire side of the body (complex hemihyperplasia), a single limb (simple hemihyperplasia), or only specific parts of a limb or body region. The condition is typically present at birth or becomes apparent during early childhood, and the degree of asymmetry may increase during periods of rapid growth. Isolated hemihyperplasia is distinguished from overgrowth syndromes such as Beckwith-Wiedemann syndrome, Proteus syndrome, or other conditions that include hemihyperplasia as one component of a broader clinical picture. However, like Beckwith-Wiedemann syndrome, isolated hemihyperplasia is associated with an increased risk of embryonal tumors, particularly Wilms tumor (nephroblastoma) and hepatoblastoma. Because of this elevated cancer risk, regular tumor surveillance is recommended, typically including abdominal ultrasound screening every three to four months until approximately age seven or eight, and measurement of serum alpha-fetoprotein levels in early childhood. The underlying cause of isolated hemihyperplasia is not fully understood, but epigenetic alterations at chromosome 11p15.5, including abnormal methylation patterns affecting imprinted genes such as IGF2 and H19, have been implicated in some cases. Most cases occur sporadically. Treatment is primarily supportive and may include orthopedic interventions such as shoe lifts or, in severe cases, surgical procedures (e.g., epiphysiodesis) to address significant limb length discrepancies. Ongoing tumor surveillance is a critical component of management.

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