Proposal of new category for congenital unilateral upper limb muscular hypertrophy.

According to congenital anomalies of the hand and forearm classifications, the common characteristic of overgrowth problems is the skeletal overgrowth of part or all of the hand. Congenital unilateral muscular hypertrophy of the upper extremity has been classified under the overgrowth (gigantism) problems as whole-limb hemihypertrophy. The common characteristic of overgrowth problems is the skeletal overgrowth of part or all of the hand, which is not prominent in these patients. Only 15 cases with this anomaly have been reported since 1962. These patients have abnormal muscles with hypertrophic appearance and changed tendon to muscle length ratio. This type of muscular hypertrophy shows an increase in the number of fibers in transverse section, as also seen in multiply innervated muscles like the sartorius and gracilis in humans. Although this phenomenon has a mosaic type distribution, there is no progression of the muscular hypertrophy during growth period. Hand deformities are not due to a part of progression of the disease but result of imbalance of the extrinsic and intrinsic muscles. The evolutionary changes of skeletal muscles should be investigated to explain this congenital phenomenon and might be classified in a different entity from the present categories.