Pseudo-Achondroplastic Dysplasia

A heterogeneous inherited chondrodystrophic growth disorder associated with disproportionate short stature and limbs, marked joint deformities, and early-onset osteoarthritis.

Pseudo-Achondroplasia; Pseudo-Achondroplastic Spondyloepiphyseal Dysplasia.

In 1969, Hall and Dorst suggested a classification into four types: two dominant (formerly designated types I and III) and two recessive (formerly designated II and IV).

4:1,000,000 live births; one of the most frequent of the skeletal dysplasias.

Both autosomal dominant of gonadal mosaicism and autosomal recessive inheritance has been reported. Gene map locus is 19p13.1.

It results as T mutations in the gene for cartilage oligomeric matrix protein (COMP). COMP produces soft cartilage, which deforms markedly under stress. Accumulation of a noncollagenous protein in the rough endoplasmic reticulum of chondrocytes and the absence of a proteoglycan “population” from the cartilage suggest that an abnormally synthesized or processed protein core is not properly transferred to the Golgi system. The structurally abnormal COMP is expressed in tendon explains the loose joints that are a consistent feature of pseudoachondroplasia.

Clinically characterized by marked shortening of the limbs with a normal head and face (which makes the difference with achondroplasia). Radiologically, all long bones are short with widened metaphyses and fragmentation, and irregularities of the developing epiphyses. In childhood, platyspondyly is characteristic, with anterior tonguing as a result of delayed ossification of the annular epiphyses; after puberty, the vertebrae become more normal in appearance. Cytoplasmic metachromasia of fibroblasts is seen under microscopy.

Patients appear normal at birth and growth retardation is seldom recognized until the second year of life when the body proportions may resemble classical achondroplasia. Skeletal lesions occur as a result of stresses on soft epiphyseal cartilage. Thus, at sites such as the anterior vertebral margins, and the wrists, ankles, and knee joints, there may be severe cartilaginous deformity. Sites not subjected to excessive stress, such as the base of skull, face, sacrum, and central portions of the vertebrae, appear relatively normal. Unlike achondroplasia, head size is normal for age and the face appears normal. Intelligence is not affected. Lumbar lordosis, kyphosis, and scoliosis may all occur. Waddling gait. There may be atlantoaxial dislocation and odontoid hypoplasia. The fingers are hyperlax and short, and do not show the trident configuration typical of achondroplasia. Ligamentous laxity contributes to the leg deformities (from genu varum to genu valgum). Chronic compression myelopathy of the cervical cord as a consequence of chronic atlantoaxial dislocation has been reported. Extraskeletal complications are uncommon. Adult height ranges from 80 to 130 cm (31.5 to 51.2 inches).

Evaluation of the stability of the atlantoaxial joint should be made (history, neurologic examination, radiographic examination including flexion/extension views, CT, MRI). Document any preoperative neurologic deficit. Thoracic dystrophy and kyphoscoliosis are present and a detailed cardiopulmonary assessment should be made (chest radiograph, echocardiography, and lung function tests).

Careful positioning of the patient is important to prevent injury to the lax joints. If atlantoaxial instability is present, procedures to ensure protection of the spinal cord must be used. Tracheal intubation with a fiberoptic bronchoscope may be preferred. Regional anesthesia had been used with success but is recommended only for those patients for whom the advantages offered by this technique outweigh those of a general anesthetic because of the potential for development of neurologic problems as a result of spinal stenosis and vertebral misalignment. Endotracheal tube size will be half to one size smaller than would be predicted for the patient's age. Postoperative ventilatory support is required for those with significant thoracic dystrophy.

Care should be taken with the use of opioids and benzodiazepines if there is any respiratory compromise.

Legg-Calvé-Perthes Disease: A group of disorders known as the osteochondroses. It is believe to be because of unexplained interruption of the blood supply to the capital femoral epiphysis resulting in avascular necrosis. Clinically, this disease is characterized by limp with or without pain in the hip, knee, thigh, and groin. Most cases occur sporadically. Other cases are thought to be inherited as an autosomal dominant genetic trait.

Multiple Epiphyseal Dysplasia (MED): A very rare genetic disorder characterized by irregular epiphyseal growth, skeletal deformities, short limb dwarfism, pain and stiffness of affected joints. There are two types of MED, a mild form or Ribbing type, and a severe form or Fairbank type. In the mild form, the hands and wrists are usually normal, whereas in the severe form, the hands and feet are short and stubby.