Achondroplasia

Overview

Board takeaway: Plan positioning and anesthesia around sleep apnea and foramen magnum stenosis. These may accompany short limbs and macrocephaly.

How does Achondroplasia affect dental management?

• Neck: Ask about foramen magnum decompression, shunts and sleep studies; keep the neck neutral and avoid hyperextension or forced flexion
• Positioning: Support the head and short limbs with pillows; a booster or positioning aids help in an adult-sized chair
• Sedation risk: obstructive sleep apnea (OSA), midface hypoplasia and possible cervical stenosis. Coordinate the setting, airway and postoperative monitoring with anesthesia. Significant OSA, neurologic compromise, or a difficult airway may require a hospital with pediatric expertise
• Occlusion: Orthodontic referral for Class III and crowding; coordinate with craniofacial care and the child’s growth pattern
• Communication: normal cognition; talk to the child at their age, not their height

Exam pearl

What is Achondroplasia?

An FGFR3-related skeletal dysplasia that impairs endochondral bone growth and causes disproportionate short stature.

What are the main systemic features of Achondroplasia?

• Genetics: The most common skeletal dysplasia (~1 in 25,000); FGFR3 gain-of-function, autosomal dominant, ~80% de novo (advanced paternal age)
• Appearance: Rhizomelic (proximal) limb shortening, macrocephaly with frontal bossing, depressed nasal bridge, midface hypoplasia, trident hand
• Neurologic risk: Foramen magnum stenosis can compress the cervicomedullary junction (central apnea, sudden death in infancy); hydrocephalus
• Airway: obstructive sleep apnea from midface hypoplasia and adenotonsillar hypertrophy
• Hearing: recurrent otitis media and conductive hearing loss
• Development: intelligence is typical; motor milestones are delayed
• Growth treatment: vosoritide (a CNP analog) is approved to increase growth
• One affected parent: when the other parent does not have achondroplasia, each pregnancy has a 50% transmission risk
• Two affected parents: counseling must also address the severe, usually lethal form caused by two altered FGFR3 copies

What oral findings occur in Achondroplasia?

• Midface (maxillary) hypoplasia with relative mandibular prognathism: Class III and anterior open bite. This reflects impaired endochondral growth of the cranial base and midface.
• Narrow, high palate with crowding; posterior crossbite
• Tongue thrust and mouth breathing from the airway pattern

For Achondroplasia, what do you ask before choosing a setting for extensive restorations?

• OSA: snoring, sleep studies, prior adenotonsillectomy; assess airway and neck
• Foramen magnum stenosis: decompression history; hydrocephalus or shunt
• Setting: base the decision on OSA severity, airway and neurologic assessment, procedure length, and rescue capability. Extensive care with significant airway or cervicomedullary risk favors a hospital and pediatric anesthesia team

Sources

• Supplemental study guide: Pediatric Dental Study Guide: Achondroplasia
• Management of Dental Patients with Special Health Care Needs
• Management of the Developing Dentition and Occlusion in Pediatric Dentistry
• Pediatric Airway Assessment
• Supplemental genetics: MedlinePlus Genetics: achondroplasia