Meromelia is defined broadly as the partial absence of at least one limb. Limb deficiencies have been known to be caused by chromosomal abnormalities, genetic disorders, environmental exposures in utero, or as a complication of chorionic villus sampling. While "amelia" refers to the complete absence of at least one limb, meromelia is just another form of the same continuum of the disorder based on severity.
In one study of congenital limb deficiencies, 64.8% of cases had an identifiable cause.
Of the 162 births with limb deformities that were considered, 13 (8.0%) were caused by chromosomal abnormalities. Trisomy 18 (Edward's Syndrome) was the most common, but also thrombocytopenia-absent radius (TAR) syndrome and trisomy 13 were observed.
14 (8.6%) of cases were caused by a known syndrome, association, sequence, or related anomaly. Vertebral defects, anal atresia, cardiac defects, tracheoesophageal fistula, renal anomalies, and limb abnormalities (VACTERL) association and anencephaly were most common in this category, while cloacal exstrophy, encephalocele, sirenomelia, prune belly syndrome, and urethral atresia were also noted.
A total of 16.1% of cases were attributed to Mendelian or familial inheritance. Ectrodactyly (i.e., cleft hand syndrome) was most common, but also Fanconi anemia, Holt-Oram syndrome, and many others were noted.
Teratogenic exposure to drugs accounted for 3.7% of cases in this study, with most resulting in infants of diabetic mothers, and one due to misoprostol exposure in utero. Take note, however, that thalidomide is classically associated with the truncation of limbs as phocomelia, and while not observed in this study is a well-known complication of the drug.
Vascular disruptions accounted for 28.4% of cases of limb defects and were most commonly caused by amniotic band syndrome. Poland syndrome and acardiac twins were other less common causes of limb deficiency.
The remaining 35.1% of limb deformities had an unknown cause.
Meromelia occurs in approximately 0.00001.4% of live births, as reported by Özdemir et al. In another review of 206,224 live births, 162 infants were identified with congenital limb deficiencies (0.079%). Of those, 101 children (62.3%) survived the first month of life. 53.7% of children with identified limb deficiencies were male, 39.5% were female, and the remainder were elective terminations where sex was not determined.
History and Physical
When a child is born with a truncated or deformed limb, practitioners should inquire about a family history of any possible inherited sources of limb deformity. One should also inquire about teratogenic exposures to drugs such as misoprostol or thalidomide, as these drugs have a known association with limb deformity.
Clinicians should perform a careful assessment for associated syndromes such as VACTERL anomalies or Fanconi anemia, which can have life-threatening consequences if left untreated. The anatomical variant will often help guide clinicians towards most likely associations, such as in the case of thrombocytopenia absent radius syndrome.
Genetic testing may be appropriate in the case of inherited disorders, or in cases of chromosomal abnormalities such as seen in Edwards syndrome (trisomy 18) or Patau syndrome (trisomy 13). Additionally, radiographs and vascular mapping of the truncated extremity is usually necessary to appropriately identify the anatomic deficiency. By appropriate understanding of each patient's anatomic abnormalities, appropriate treatment and prosthetics can be provided.
Over half of the cases of meromelia have a known association or underlying cause. Edward syndrome or trisomy 18 is the most common chromosomal abnormality associated with congenital limb defects. Similarly, a deletion on chromosome 1 can lead to thrombocytopenia absent-radius syndrome.
Ectrodactyly and Fanconi anemia are commonly inherited disorders associated with meromelia in children. Non-inherited associates such as VACTERL association frequently appear in conjunction with limb truncation deficits as well.
Gold et al. found that of 162 births with congenital limb deformities, 101 (or 62.3%) were liveborn and survived the first month of life, whereas 10 (or 6.2%) were liveborn but did not survive the first month, 17 (or 10.5%) were stillborn, and 34 (or 21%) were elective terminations. That being said, those who survive with limb truncation deformities typically have a high functional status, and generally, depending on the severity of their deformity can care for themselves very effectively with appropriate therapy and prosthetics.
Most life-threatening complications associated with limb truncation defects will be due to associated anomalies. For example, meromelia frequently presents in conjunction with VACTERL association, as discussed above, and the associated cardiovascular, intestinal, renal, and other congenital defects can result in a whole slew of complications. Those with Fanconi anemia have a high risk of aplastic anemia. TAR syndrome, as the name suggests, may also have hematologic consequences in the form of thrombocytopenia.
Deterrence and Patient Education
Increased drug regulatory practices may reduce the incidence of limb deformities associated with misoprostol and thalidomide. Additionally, uncontrolled diabetes may have a teratogenic effect, and therefore appropriate prenatal care and diabetes management may also have an effect on decreasing the number of limb deformities. Even in the setting of these teratogenic causes, meromelia is extremely rare, and many cases are unavoidable. Therefore, if a child is found to have a limb truncation defect, a thorough evaluation is necessary to optimize patient survival and management. Parents should have their child evaluated by an appropriate primary clinician, geneticist, cardiologist, nephrologist, and/or gastroenterologist depending on relevant associated conditions. Furthermore, physical and occupational therapy can play a substantial role in maximizing patient function.
Enhancing Healthcare Team Outcomes
Congenital limb defects can be devastating for parents, but many patients can have very functional, otherwise normal lives. As with any congenital deformity, appropriate care begins in the prenatal period. Appropriate obstetric care, prenatal screenings, and avoidance of teratogenic drugs is the first step to minimizing the risk of congenital deformity. For children with genetic or unknown causes of limb defects, an interprofessional team consisting of various specialists outlined previously in conjunction with appropriate therapists, nurses, and clinical staff must work together to identify risk factors for morbidity and mortality and effectively avoid complications. [Level 5]