Pseudoachondroplastic dysplasia.A Khungar, P Mahajan, G Gupte, M Vasundhara, A Kher, BA Bharucha
Dept of Pediatrics, Seth GS Medical College, Bombay, Maharashtra.
Pseudoachondroplasia is a heterogeneous inherited skeletal dysplasia in which dwarfism is a major feature. We report here a case of a 7 year old girl misdiagnosed as rickets, who presented with short stature, lordosis, genu varum and flexion deformities at both the elbows. Skeletal survey revealed epiphyseal and metaphyseal irregularities. A review of literature is also presented.
Keywords: Achondroplasia, complications,diagnosis,genetics,Case Report, Child, Diagnosis, Differential, Diagnostic Errors, Dwarfism, complications,diagnosis,genetics,Epiphyses, abnormalities,Female, Heterozygote, Human, Osteochondrodysplasias, complications,diagnosis,genetics,Rickets, diagnosis,
Osteochondrodysplasias characterized by involvement of the spine, epiphyses and metaphyses can be divided into spondylo-epiphyseal, spondylo metaphyseal and spondylo-epimetaphyseal dysplasias. Pseudoachondroplastic spondylo-epiphyseal dysplasia is a term first used in 1959 by Maroteaux and Lamy' and later by Rubin to describe a category of bone dysplasia which combines features of both achondroplasia and sponclylo-epiphyseal dysplasia.
PS a 7-year-old girl, born of a non-consanguinous marriage was referred to the Genetic clinic for detailed investigation of short stature. She was apparently well till 1 year of age, when mild bowing of the legs was noticed by the parents which gradually increased. She was treated as a case of rickets with multiple doses of vitamin D by number of physicians, whom she approached after the age of 3. Her metabolic parameters (Ca, P, alkaline phosphatase, renal chemistry, venous bicarbonate and urine pH) were consistently within normal limits. Urine Ca and P excretion were normal. Mucopolysacchariduria was absent.
On examination [Figure:1] the child had severe short stature with a height of 98 cms (< 5th percentile, height age 3 ½ yrs by ICMR standards). Upper to lower segment ratio was 1.68 suggesting short limbed dwarfism. Intelligence quotient was normal. The head was not large and appeared normal without the typical facies of achondroplasia. There was no corneal clouding. There was marked lumbar lordosis with a waddling gait, genu varum and epiphyseal widening. A fixed flexion deformity of 15-20? at both elbows was present associated with hypertension at wrists and fingers. Systemic examination was normal.
A complete roentgenographic skeletal survey was performed which revealed generalized epiphyseal and metaphyseal irregularity with limb shortening, flaring and spurring at the metaphyses. X-rays of the spine showed irregularity of the end plates with anterior, central beaking and flattening of vertebral bodies. Pelvic X-rays revealed widened iliac and acetabular index with irregularity of the acetabulum [Figure:2].
There was delayed pelvic maturation with deficient ossification of the anterior pubic arch associated with coxa valga and a pointed hypoplastic caudal segment of the pelvis. X-ray knees showed metaphyseal and epiphyseal irregularity with spurring and bilateral genu varum [Figure:3]. Hand X-rays revealed a mild Madelung deformity and the metacarpals were short and wider than normal. X-ray skull was normal.
Urine electrophoresis for mucopolysaccharides was negative. The height of the parents and the younger sib was within normal limits.
Pseudoachondroplasia (PsA) is a type of short-limbed dwarfism which is half as frequent as classical achondroplasia. Its frequency is about 4 per million population.
A number of cases have been described in literature,, including the one reported form our genetic clinic in 1981. It is usually recognized in early childhood after the development of gait disturbances or knee deformities. Clinical features include joint laxity, limitation of elbow extension, genu varum or valgurn and moderate lumbar lordosis. The facies, intelligence and life span are normal.
Hall and Dorst defined 4 types of PsA in their classification.
The eponym of Kozlowski was associated with the mild types I (McKusick No. 17715) and II (McKusick No. 26415), and that of Maroteaux-Lamy with the severe types lit (McKusick No. 17717) and W (McKusick No. 26416). According to this classification, types I and III were inherited as autosomal dominant, while types II and IV were autosomal recessive. Type IV is the most severe form with severe limb shortening. Associated anomalies like marked joint laxity and instability are commoner in the autosomal recessive forms. Sporadic cases have been reported, and presumably represent fresh mutuations. Although this classification is not universally accepted, diagnostic precision is important, otherwise genetic counselling is unrealistic and inaccurate.
In this disorder, a marked alteration in metabolism most likely produces soft cartilage that can deform markedly under stress. The skeletal lesions are best explained as deformations, which result when normal stresses are applied to soft epiphyseal cartilage. At sites protected from excessive stress such as the base of skull, face, sacrum and neurocentral plates of vertebrae, relatively normal enchondral ossification prevails. However, at sites under great stress such as the anterior vertebral margins, knee joints, ankles and wrists, the cartilage may become severely deformed. Severe disorganization of the growth plates may explain the short diaphyses seen in the disease. The skeletal anomalies progress throughout childhood, but improve with skeletal maturity. Cooper et al studied cartilage from affected patients and demonstrated a specific ultra-structural defect-a storage in the rough endoplasmic reticulum of inclusions and whorls with alternatively electrondense and electron-luscent layers which they believed to be an abnormal protein, perhaps lipoprotein or glycoprotein.
The bow leg deformities, which are a common feature of PsA may lead to a misdiagnosis of vit D resistant rickets; and the metaphyseal irregularities to a misdiagnosis of metaphyseal chondrodysplasia.
As PsA is not clinically or radiologically evident until early childhood, it does not enter into the differential diagnosis of the newborn short-limbed dwarfs. PsA must be differentiated from achondroplasia, spondylo-epiphyseal dysplasia and Morquio syndrome. The chief features that differentiate PsA from classic achondroplasia are 1. late discovery of the abnormality, 2. absence of clinical or radiologic abnormalities in the face and skull, 3. radiologic findings of gross irregularities in the epiphyseal-metaphyseal areas with fragmentation of the epiphyseal ossification centres.
These patients are intellectually normal and adult height varies between 82-130 cm. The main disability is due to secondary osteoarthrosis of hip and knee. Corrective osteotomy for gross deformities may be done after the growth period. Arthroplasty may be tried in adults.
Though considerable heterogeneity exists with mild to severe types, and classification purely on radiological appearances is not possible in all cases, knowledge of the genetic background and awareness of the stigmata of the various types helps the effective management and genetic counselling. However, such genetic counselling in our patient was particularly difficult as she was moderate severely affected with no family history of a similar disease.
We wish to thank Dr. PM Pai, Dean, King Edward Memorial Hospital, Mumbai for granting permission to publish this case report.