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Metaphyseal Chondrodysplasia (Dysostoses)

- Discussion:
    - heterogeneous group of intrinsic dysplasias characterized by x-ray changes in the metaphysesof the short and long tubular bones 
          (epiphyses remains normal);
    - defect appears to lie in proliferative & hypertrophic zones of physis;
    - hypercalcemia is common;
    - diff dx:
          - many pts will initially thought to have a hypophosphatemic vit D-resistant rickets, which can lead to the innappropriate administration 
                 of Vit D;
    - associated disorders:
          - metaphyseal chondrodysplasia may be associated w/ neutropenia, lymphopenia, immune deficiency, pancreatic exocrine 
                 insufficiency, hirschsprung's disease, and intestinal malabsorption;

- Clinical Presentation:
    - condition is first recognized in early childhood when children present with a waddling gait, exaggerated lumbar lordosis, genu varum, and 
            short stature;
    - additional features include:
           - mental retardation;
           - joint contractures;
           - exophthalmic eyes;

- Histology:
    - defect appears to lie in proliferative & hypertrophic zones of physis;
    - light microscopy reveals cell clusters or nests rather than normal columnization;
    - zone of provisional calcification narrows with irregular vascular invasion, resulting in islands of unmineralized cartilage extending into the 

- Radiographs:
    - radiographic appearance of an enlarged metaphysis & widened cupped physis is similar to rickets;
    - coxa vara occurs without an associated bowed femur;
    - it is treated w/ valgus intertrochanteric osteotomy when progressive;
    - genu varum may be severe in the Schmid type.

- Schmid type:
    - this disorder may arise from defective type X collagen, which is typically found in the hypertrophic zone of the physis;
    - patients show mild short sature, leg pains, bowed legs, increased lordosis, and waddling gait;
    - upper extremity:
           - mild wrist swelling;
           - flexion contractures of the elbows;
    - lower extremities
           - more significantly involved than upper extremities;
           - varus deformities of the knees and ankles are prestent, with bowing visible in both the thigh and the leg;
           - genu varum may be severe in the Schmid type;
           - surgical correction should be delayed until it is determined that spontaneous correction will not occur.

- Metaphyseal Dysplasia (Pyle's Disease)
    - autosomal recessive disorder which manifests at a variable age;
    - mild clinical symptoms and signs, including joint pain muscular weakness;
    - scoliosis, genu valgum deformity, dental / malocclusion and bone fragility;
    - marked expansion of the metaphyseal segments of tubular leads to an "Erlenmeyer flask" appearance, esp in the distal femur and 
            proximal tibia and fibula

A constitutively active mutant PTH-PTHrP receptor in Jansen type metaphyseal chondrodysplasia.

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