Teaching Case

A 6-month-old boy presented with gradual and progressive enlargement of the right upper limb since birth, especially the right hand involving the middle three fingers. He had difficulty in thumb opposition and resultant functional disability. There is associated clinodactyly of right thumb with syndactyly of the middle and ring fingers.

Radiograph demonstrated increased soft tissue component of right hand compared to the contralateral side, especially the middle three fingers with associated increase in the length and width of corresponding metacarpals and phalanges. There is syndactyly of the middle and ring finger with bony fusion of the distal phalanges.

MR and CT of the right upper limb revealed atrophy of the muscles of the arm and forearm with lipomatous hypertrophy of the subcutaneous tissue.

Background

Macrodystrophia lipomatosa (ML) is a rare congenital cause of limb gigantism due to hamartomatous growth of fibrofatty tissue involving single or multiple digits or the entire limb. It is interchangeably also called macrodactyly, digital gigantism, macromelia or limited gigantism [1].

Clinical Perspective 

ML can present anywhere from neonatal period to late adulthood. The growth reaches a plateau at puberty. It commonly involves the lower limb, predominantly the medial aspect (along plantar nerve distribution). In the upper limb, involvement of lateral aspect is common (along the median nerve distribution) [2,3]. The primary pathology is increase in adipose tissue scattered in fibrous tissue, involving the bone marrow, periosteum, muscles, nerve sheaths and subcutaneous tissues with irregular enlargement of the median nerve in hand or plantar nerve in the foot [4].  Multiple periosteal nodules comprising chondroblasts, osteoblasts, and osteoclasts are seen coalescing towards distal ends of phalanges resulting in elongated phalanges with splayed distal ends.

ML patients usually present with cosmetic and mechanical problems. Soft tissue overgrowth is commonly seen in the volar aspect with dorsal deviation of the hand thus interfering with day-to-day activities. Also, mechanical problems like secondary osteoarthritis (reduced joint space, subchondral cysts, osteophytes) and compression of neurovascular structures can be seen (carpal tunnel/ tarsal tunnel syndrome) resulting in functional impairment [5].

Imaging Perspective

Radiographic findings of ML include excessive soft tissue and osseous overgrowth, radiolucent fatty areas and degenerative joint disease. Excessive bone growth and fat proliferation within muscle fibers are characteristic on CT. Widening at the distal end of the bones gives a characteristic mushroom-like appearance [6]. MRI can easily demonstrate fatty infiltration of muscles, hypointense fibrous bands, osseous hypertrophy and fibrous nerve thickening.

Outcome 

Management aims at improving cosmetic appearance while preserving neurologic function. Surgical intervention is indicated depending upon the patient's symptoms, age, extent and severity of the disease. In a localized disease, ray removal is done. Other interventions like multiple debulking procedures, epiphysiodesis and various osteotomies are indicated for a more severe form of the disease. The surgical treatment is, however, quite challenging as despite adequate tissue removal, the difference in size may not be very apparent. Besides, the incidence of nerve injury following extensive debulking is approximately 30%-50% with a high recurrence rate of 33%-60% [7].

Take Home Message / Teaching Points

ML is progressive hamartomatous growth of fibrofatty tissue involving soft tissue and bone leading to localized gigantism. Diagnosis is made on the basis of clinical and radiological evaluation, which can be confirmed on histopathology. The management is mainly surgical but the outcome may not be very gratifying.