Pycnodysostosis in an Adult: A Case Report and Review of the Literature

Pycnodysostosis is a rare sclerosing bone dysplasia with manifestations in the head and neck that should be considered by a treating otolaryngologist. Pycnodysostosis is caused by an autosomal recessive mutation in the cathepsin K gene. ¹ Deficiency of this enzyme causes poor resorption of bone matrix and results in diffuse osteosclerosis. Patients with pycnodysostosis usually present in early childhood with dwarfism, acro-osteolysis of fingers, and skull deformities with delayed suture closure.

We present a 31-year-old male patient with a history of pycnodysostosis, mild mental retardation, diabetes mellitus, osteomyelitis of the left mandible, morbid obesity, and obstructive sleep apnea, who presented with right jaw pain. Noncontrast computed tomography of the maxillofacial bones demonstrated hypoplastic maxillary, frontal, and sphenoid sinuses. The orbital volume appeared to be relatively reduced bilaterally as a result of expansion of the surrounding bone, resulting in exophthalmos (Figure 1). There was marked, diffuse osseous thickening and sclerosis of the facial bones and skull base consistent with the known history of pycnodysostosis. Multiple deformities were observed in the maxillary and mandibular deciduous teeth, some of which were unerupted (Figure 2).

Figure 1.

Noncontrast CT scan demonstrating hypoplastic sphenoid sinuses, under-aerated mastoid air cells, and orbits surrounded by sclerotic bone with exophthalmos are seen on axial bone algorithm. CT indicates computed tomography.

Figure 2.

Noncontrast CT of the facial bones demonstrating sclerotic intramedullary density in the right maxillary bone (arrows), which likely represents an unerupted deciduous tooth, without surrounding apical cyst formation. CT indicates computed tomography.

Pycnodysostosis is inherited as an autosomal recessive trait, and many patients have either a positive family history or consanguineous parents. In patients without a known history of pycnodysostosis, the differential diagnosis should include sclerosing bony dysplasias such as cleidocranial dysostosis and osteopetrosis. Pycnodysostosis often presents in childhood with short stature, but various phenotypic expressions have been reported. ² Prominent head and neck features include an obtuse mandibular angle, bossing of the skull, open fontanels and sutures, and crowding and impaction of the teeth. Patients often demonstrate a grooved palate and mid- and lower-facial hypoplasia ^3,4 (Figure 3). These bony deformities often contribute to obstructive sleep apnea.

Figure 3.

The patient demonstrates an obtuse mandibular angle as well as mid- and lower face hypoplasia on 3D reconstructed noncontrast CT scan. CT indicates computed tomography.

Patients may also present with delayed loss of deciduous dentition and associated dental complaints. Patients characteristically demonstrate hypoplasia of the alveolar ridge and dental crowding. ⁵ The follicles of unerupted teeth can become secondarily infected and form abscesses, with a propensity for developing osteomyelitis. ^2,4 This increased risk of osteomyelitis is often attributed to a decrease in the intramedullary space and resulting predisposition to vascular compromise. ^6,7 Midface and mandibular bony hypoplasia contributes to craniofacial dysmorphism as well as upper airway obstruction in many patients with pycnodysostosis ⁵ (Figure 4). One group described bimaxillary orthognathic surgery as the treatment of choice to improve occlusion and facial aesthetics. ⁸

Figure 4.

Noncontrast CT of the facial bones demonstrating congenital narrowing of the posterior nasal airway (arrows), which likely contributes to the patient’s known obstructive sleep apnea. CT indicates computed tomography.

Pycnodysostosis is a rare autosomal recessive condition that requires a multidisciplinary team for appropriate lifelong management. Here, we highlight the characteristic maxillofacial radiologic findings of the disease and their clinical importance. These findings are critical to identify the appropriate diagnosis, as there is a limited but significant differential diagnosis composed of other sclerosing bone dysplasias. Awareness of the key manifestations and natural history of this inherited disorder will facilitate the prevention and treatment of common complications.