A 17-year-old girl was referred for taking hand X-ray to check the epiphysis as she had short stature with short finger and toes (Fig. 1a, 1b) and was suspected for low level growth hormone. She also had abnormal teeth, mild proptosis, beaked nose, prominent cranium with frontoparietal bossing.
Hand X-ray showed hyperostosis of bones with partial agenesis of first, second and third distal phalanges (Fig. 2). In order to investigate more and rule out any other bony anomalies, skull X-ray and lumbosacral spine X-ray of the patient were taken after obtaining consent from the patient and her elder sister. Skull X-ray in lateral projection demonstrated enlarged head, thick calvarium, frontal bossing, open coronal and lambdoid suture with wormian bones in the lambdoid suture, shallow mandibular angle with mild-mandibular prognathism and hypoplasia of paranasal sinuses (Fig. 3). In the lumbosacral spine X-ray osteosclerosis of vertebral bodies and visualised parts of pelvis and ribs were observed. Lose of lumber spine normal lordosis with mild kyphotic changes of the upper lumbar spine were seen. Underdevelopment of the upper endplates of L2, L3 and L4 with possible spondylolysis of L5/S1 were also noted. (Fig. 4).
Pyknodysostosis is an autosomal recessive disease of extensive increased bone density. This is a lysosomal storage disorder which is caused by the mutation of a gene responsible for cathepsin K resulting in cathepsin deficiency relevant chromosome 1q21. The cathepsin K is a protease enzyme necessary for normal osteoclast function and degradation of type 1 collagen which produces 95% of the bone organic matrix. With the lack of this enzyme decreased bone resorption occurs which results in increased bone density [1].
The disease is usually diagnosed by typical clinical and radiographic features; however, an exact confirmation is obtained from the analysis of cathepsin kinase gene mutation [2]. The patients have short stature with a height of 150 cm or less, short limbs, wrinkled skin, kyphosis, scoliosis, history of repeated chest infections, mild enlarged head with a beaked nose, slight proptosis and sleep apnea. In the skeletal X-ray general increased bone density is seen. Hand X-ray demonstrates osteosclerosis with acro-osteolysis of the terminal phalanges. In the skull X-ray thick calvarium, frontoparietal bossing, open fontanelles and sutures with wormian bones in the lambdoid suture, hypoplasia of paranasal sinuses, obtuse mandible angle, mandibular prognathism and persistent primary teeth can be appreciated. Sclerosis of vertebral bodies, clavicle hypoplasia with erosion of distal parts can also be detected [3].
In this case, many typical radiographic features of Pyknodysostosis are present while contrary to the literature instead of increased lumbar lordosis which is typical for the disease, loss of normal lordosis with mild kyphosis of the upper lumbar spine is seen. The treatment of Pyknodysostosis is usually supportive including prevention of bone fractures and dental hygiene. The regular dental check-up is helpful to avoid dental problems. Special cares should be taken during a tooth extraction procedure to reduce the rate of infection and decrease mandibular fracture. Some patients may get long bone fractures as well as mandibular fractures commonly caused by post-osteomyelitis, trauma and exodontia. The intellectual and sexual development of patients is usually normal. This anomaly always has a good prognosis and the patients have good life expectancy [4]. In conclusion, the early diagnosis of patients with Pyknodysostosis with their typical clinical and radiographic features would help to avoid unnecessary treatments. Alternatively, the physicians should advise patients to take specific precaution to prevent bone fracture during exercise and recommend particular dental hygiene. Also, parents need specific guidance regarding handling their affected children.
Pyknodysostosis
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(1) From the hand and foot photos, it is evident that both the fingers and toes are relatively short, showing underdevelopment at the distal ends, with phalanges that appear comparatively short.
(2) Hand X-ray shows: overall increased bone density (local areas may show osteosclerosis), and some distal phalanges exhibit morphological changes or mild bone resorption that is not clearly evident.
(3) Lateral skull X-ray demonstrates thickening of the skull vault, frontoparietal bossing, less pronounced midfacial prominence, and a somewhat “beaked” shape to the nasal bridge. There may be abnormal dental development, potentially involving delayed eruption or irregular alignment of some permanent teeth.
(4) Lateral view of the spine reveals reduced or absent lumbar lordosis, with mild kyphosis in certain areas (i.e., mild backward curvature in the upper lumbar region or a gentle kyphotic curve in the thoracolumbar area). The vertebral bodies also appear to show increased density.
Based on the clinical presentation (short stature, short fingers and toes, abnormal dentition, craniofacial features) and radiological indications of increased bone density, skull thickening, and abnormal phalangeal shape, the main considerations include:
Given the presence of short fingers and toes, increased bone density, frontoparietal bossing, dental abnormalities, and the “beak-shaped” nose, along with evident osteosclerosis and distal phalangeal changes on X-ray, the most likely diagnosis is:
Pyknodysostosis (致密性骨营养不良).
For definitive confirmation, additional genetic testing (analysis for cathepsin K gene mutations) or specialized evaluations (endocrine assessments, bone metabolism markers, etc.) could be pursued.
(1) Treatment and Follow-up:
• Current management is primarily supportive and symptomatic, focusing on fracture prevention and dental health protection.
• Regular follow-up and dental care are recommended to prevent gingivitis and periodontitis. If tooth extractions or dental surgeries are required, adequate safeguards and infection control measures should be taken to reduce the risk of jaw fracture.
• For patients at high risk of fractures, reinforce safety measures to avoid intense impacts or falls.
• If there is limited range of motion or bone deformity, consultation with an orthopedic specialist is advised to evaluate the need for corrective surgery or supportive bracing.
(2) Rehabilitation and Exercise Prescription:
Due to increased bone fragility from the condition, exercise should be introduced gradually under safe conditions, following the FITT-VP principle (Frequency, Intensity, Time, Type, Progression, Volume):
Ideally, begin with joint mobility and core stability exercises, then progressively incorporate light resistance or aerobic activities (e.g., stationary biking or aquatic therapy). Ensure these activities are supervised by a specialist or rehabilitation therapist for safety.
This report provides a reference analysis based on the current imaging and patient history and does not replace an in-person consultation or professional medical advice. Please consult the relevant specialists for comprehensive and accurate assessments that combine clinical and laboratory findings.
Pyknodysostosis
