Phocomelia
- Article Author:
- Donald Davis
- Article Editor:
- Steven Kane
- Updated:
- 6/25/2020 1:14:51 PM
- For CME on this topic:
- Phocomelia CME
- PubMed Link:
- Phocomelia
Introduction
Phocomelia is a rare congenital defect defined by the absence of intermediate segments of the extremity. Children with phocomelia present with their hands or feet directly attached to the trunk. Phocomelia is famously a teratogenic side effect of the drug "thalidomide," a drug first marketed to treat anxiety and morning sickness. Despite claims that the drug was safe during pregnancy, it was removed from the market in the 1960s when clinicians noted an association with phocomelia. Forty percent of patients affected by the teratogenic effects of thalidomide died near the time of birth. These congenital disabilities had a profound social and political impact on drug regulation and proof of safety.[1][2]
Etiology
While phocomelia is the most notable side effect of thalidomide, there have been several cases in the last 30 years of phocomelia associated with thalidomide use. However, today the cause of most cases is undetermined. Despite strict regulation worldwide, there have been several cases in the last 30 years of thalidomide attributed phocomelia. Underdeveloped countries and those endemic with leprosy where thalidomide occasionally remains in use, still report cases of defects caused by thalidomide exposures in pregnancy. Strict regulations in more developed countries have resulted in a dramatically decreased incidence of phocomelia within the general population.[3][4]
Aside from the teratogenicity of thalidomide, researchers have hypothesized that phocomelia is associated with anomalous origins of the subclavian artery, resulting in a disrupted vascular supply to intermediate limb segments.[5][6]
Epidemiology
The incidence and presentation of phocomelia were examined in 22,740,933 live births by Bermejo-Sanchez et al. in an effort to assess the prevalence of true phocomelia. Reports indicate that true phocomelia occurs in 0.62 live births per every 100,000 patients. Approximately half (53.2%) of the cases displayed isolated phocomelia, while 36.9% had additional major congenital abnormalities, and 9.9% of cases correlated with a clinical syndrome.
The data shows that 55.9% of cases only involve one limb, while 40.2% of cases only involved two limbs. Only four cases of 141 had involvement of all four limbs. When comparing single upper extremities deficiencies, the left side was more commonly affected (64.9%) than the right.
When two limbs were involved, the upper limbs were involved 58.5% of the time compared to the lower limbs. The incidence of these findings was lower than what prior studies had reported, which is likely due to the care taken by this study, only to consider true phocomelia and not amelia or other limb truncation.[1][7]
Pathophysiology
In extremity development, the apical ectodermal ridge forms at the most distal end of the limb bud. This apical ectodermal ridge through its interaction with the underlying progress zone mesoderm subsequently determines appropriate longitudinal growth of the extremity, as well as differentiation of distal and proximal structures of the limb bud. Cell death due to apoptosis from any cause such as vascular insufficiency or drug toxicity that interrupts this relationship between the apical ectodermal ridge and the progress zone can result in phocomelia.[8]
History and Physical
Any time phocomelia is identified in a newborn, and given its correlation with thalidomide, practitioners should inquire about medications taken during early pregnancy. Additionally, children should undergo a thorough physical examination as one study reported that 36.9% of phocomelia cases have additional major malformations, with 9.9% of cases being attributable to various syndromes.[1]
Evaluation
When phocomelia is identified in a child, physicians should complete a thorough search for other associated abnormalities, as other defects are present in approximately half of the patients presenting with this limb anomaly. Particularly, practitioners should examine the musculoskeletal system, including the vertebrae, the intestines, and the heart, as dysfunction in these organ systems appears most frequently in conjunction with phocomelia.[1]
Treatment / Management
The most important management of a child born with phocomelia is to assess for other associated abnormalities, especially of the heart and intestines, and address them promptly and appropriately. Pediatric cardiologists and gastroenterologists should examine the child and recommend a treatment plan for any abnormalities encountered.
From the perspective of the hypoplastic limb, prosthetics may be of some use, but many without concomitant pathology can function quite well. Families of children who have severely hypoplastic extremities should work with therapists to help understand how to meet the unique needs of their children. And finally, caring for a disabled child can be traumatic for some people. Therefore, physicians should have a low threshold to recommend mental counseling services to assist in coping mechanisms that may be needed by both the parents and the child.
Differential Diagnosis
Bermejo-Sanchez et al. report that 9.9% of cases of phocomelia are associated with different syndromes. They appear here in order of decreasing prevalence[1]:
Roberts Syndrome: A rare autosomal recessive disorder caused by a mutation in the ESCO2 gene that manifests with severe limb malformations and craniofacial defects.[9]
Thrombocytopenia with radial aplasia (TAR): A rare autosomal recessive disorder related to the RBM8A gene that presents with thrombocytopenia and limb radial deficiency.[10]
Syndrome of severe limb defects, vertebral hyper-segmentation, and mirror polydactyly: An autosomal recessive disorder resulting in severe limb hypoplasia with polydactyly and hypersegmentation of the spine.[11]
Prognosis
In one review study, there were 85 live births to every 24 stillbirths for children with phocomelia. When considering only cases of isolated phocomelia, there were 57 live births to every eight stillbirths.[1]
Complications
Children with phocomelia have a high stillbirth rate compared to the general population. Furthermore, children with severe limb hypoplasia may or will face problems with activities of daily life and mobility. For this reason, health care teams must be integrated to provide for more than just the medical challenges that present with phocomelia.
Deterrence and Patient Education
Increased drug regulatory practices across the world have significantly decreased the incidence of thalidomide induced limb hypoplasia. Thalidomide has utility in the treatment of insomnia, anxiety, and even in the treatment of leprosy, but understanding the risks of thalidomide exposure during pregnancy is critical for any woman taking the medication. Patients and prescribers alike should understand the deleterious effects of thalidomide when taken in early pregnancy.
Enhancing Healthcare Team Outcomes
Phocomelia and the thalidomide controversy was a critical step forward in the regulatory practices of pharmacology. The most important responsibility of the healthcare community, regarding phocomelia, is the prevention of prescribing of unsafe medications that can cause limb truncation; this occurs through careful prescribing practices and thorough patient education.
For patients born with limb hypoplasia, as is seen in phocomelia, an interdisciplinary team of specialists needs to examine the patient to screen for associated abnormalities that may be fatal, as half of the patients with phocomelia and amelia have associated defects. As many related abnormalities of the heart, vertebrae, or other vital organs may be life-threatening, these anomalies should be addressed promptly by consulting physicians. If surgical intervention is required, a dedicated OR team, including a nurse, scrub technician, and surgical assists, must be well-versed in any operative plan and work efficiently as a team to optimize patient outcomes.
Finally, a prosthetist and therapist can help a developing child with disabilities to function at a higher level. Families caring for disabled children are often under tremendous financial and emotional strain. Therefore, appropriate mental health counseling and social work may be necessary for caring not only for the patient but for their families as well. [Level 5]