Dipygus is a rare and complex congenital condition characterized by the duplication of the lower half of the body. It is often classified as a form of conjoined twinning, where the body’s developmental axis forks, leading to a single torso with duplicated posterior structures.
The Developmental Origins of Dipygus
The formation of dipygus results from the incomplete division of a single embryo during its earliest stages, not the fusion of two separate embryos. This process occurs within the first two weeks after fertilization due to a disruption along the body’s developmental axis at the caudal (tail) end. This disruption is thought to affect the embryonic cloaca and notochord, which are structures that guide the formation of the lower body.
In dipygus, the embryo’s developmental blueprint splits at its lower end, causing the duplication of lower body structures while the upper body remains single. This event is described as an “uninhibited fission of the germinal disc at the caudal end and arrested fission rostrally.” The precise trigger for this forking is not fully understood but is believed to involve a combination of genetic and environmental factors.
This partial division results in caudal duplication syndrome, with dipygus being its most severe form. The developing embryo begins to form two lower halves, and the degree of this duplication varies significantly, accounting for the wide range of presentations.
Physical Manifestations and Diagnosis
The most apparent physical manifestation of dipygus is the presence of four legs due to a duplicated pelvis and lower limbs. The extent of duplication varies; some individuals have two well-formed outer legs and two smaller, less-developed inner legs that may not be functional for walking.
Internal duplication commonly affects the genitourinary and lower gastrointestinal tracts. An individual with dipygus may have two separate pelvises, two bladders, two urethras, and duplicated reproductive organs. The lower spine can also be duplicated, starting from the lower thoracic or lumbar region downwards.
Diagnosis is frequently made before birth using prenatal ultrasound, which can reveal extra limbs and an abnormal pelvic structure during second-trimester scans. After birth, imaging studies like Magnetic Resonance Imaging (MRI) and Computed Tomography (CT) scans provide a detailed view of the internal anatomy. These scans are necessary to understand the full extent of the duplication and plan any required management.
Notable Historical and Modern Cases
The most famous historical case of dipygus is Josephine Myrtle Corbin, born in 1868. She had two separate pelvises from the waist down, resulting in four legs. Each of her smaller inner legs was paired with an outer leg; she could move the inner legs, but they were too weak for walking. One of her normal-sized feet also had a clubfoot deformity.
At age 13, Corbin began a career in the sideshow circuit as the “Four-Legged Girl from Texas.” Her unique anatomy made her a popular attraction, and her fame reportedly inspired fraudulent four-legged exhibits.
At 19, Corbin married a doctor named James Clinton Bicknell and had five children. Medical journals documented her pregnancies, noting she carried children in her separate uteri, with three conceived on one side and two on the other. She passed away in 1928 at age 59 from a skin infection. To prevent grave robbers, her family encased her casket in concrete.
Medical Management and Surgical Interventions
Medical management for dipygus is highly customized to the specific anatomical duplications and functionality of the limbs and organs. A multidisciplinary team of specialists, including pediatric and orthopedic surgeons and urologists, creates a comprehensive care plan. The goals are to address life-threatening issues and improve functional ability and quality of life.
Surgical intervention is a common component of management. Underdeveloped or non-functional supernumerary limbs may be surgically removed, which can be a complex procedure if duplicated pelvic bones are involved. Reconstructive surgery is also often necessary for duplicated urinary and gastrointestinal systems. For example, surgeons may combine two bladders or reconstruct the external genitalia.
Not all cases require extensive surgical correction. If duplicated organs are functional and cause no health problems, a conservative approach may be taken. The focus then shifts to managing issues like urinary tract function or orthopedic challenges. Long-term care often includes physical and occupational therapy to improve mobility.