Pediatric Rheumatology Online
Journal
Vol. 2, No. 1 (105-106 ) 2004
Answer
to Previous Fellow's Challenge Case
The child presented as the clinical challenge in volume 1, number 2, has a diagnosis of
Morquio syndrome (Mucopolysaccharidosis IV or MPS IV). This autosomal recessively inherited storage
disease is associated with accumulation of keratin sulfate secondary to an
enzyme deficiency of either galactosamine-6-sulfatase (Morquio syndrome A) or
ß-galactosidase (Morquio syndrome B).
Urine testing reveals increased excretion of keratin sulfate in both
Morquio sub-types. Our patient was
diagnosed by skin biopsy to have Morquio syndrome B which is generally less
severe than Morquio syndrome A, although there is considerable phenotypic
overlap.
Clinically, these children present during their
second to fourth year of life with multiple musculoskeletal abnormalities. Prominent features are short-spine dwarfism,
overall growth delay, and significant loss of joint range of motion with
occasional mild joint swelling. They
generally develop a pectus carinatum deformity, kyphoscoliosis, genu valgum and
pes planus. Physical deformities
progress with age. A major skeletal
complication is atlanto-axial instability which results from hypoplasia of the
odontoid process. Surgical fusion of the
upper cervical spine is often indicated.
Other clinical involvement includes corneal clouding and impaired
hearing. Intelligence is normal. Patients generally survive into adulthood,
but life expectancy is limited.
Radiographic findings in Morquio syndrome help to
direct the clinician toward the making this diagnosis. Dysostosis multiplex is the term often used
to describe the array of x-ray abnormalities seen in Morquio syndrome and other
storage diseases. Vertebral changes are
prominent. Platyspondyly of the thoracic
and lumbar vertebrae is present, often with central anterior bony protrusion of
the verterbral bodies. Cervical spine x-rays
often reveal odontoid hypoplasia and atlanto-axial instability. Hip radiographs show a coxa valga
deformity, flattening of the femoral heads and
hypoplasia of the lateral aspects of the acetabulum. Radiographs of the hands, with a classic
abnormal metacarpal appearance, suggest the diagnosis of a storage disease. Metacarpal bones usually have diaphyseal
widening and brachymetacarpia. In
Morquio syndrome, the proximal ends of the metacarpal bones tend to be
conically shaped.
The differential diagnosis of Morquio syndrome always
includes spondyloepiphyseal dysplasia (SED) congenital. Clinical similarities include dwarfism with a
short spine, pectus carinatum, kyphoscoliosis and genu valgum. Radiographic similarities include odontoid
hypoplasia and platyspondyly. Although
the vertebral findings in SED and Morquio syndrome look similar to the
rheumatologist, the radiologist can often note differences in the vertebral
appearance which are more characteristic of one diagnosis versus the
other. For the clinician, the easiest
way to differentiate radiographically between Morquio syndrome and SED is to
note the marked metacarpal changes in the former, in contrast to the relatively
normal appearance of these bones in SED.
All the fellows responding to this Fellow’s Clinical
Challenge selected spondyloepiphyseal dysplasia as the diagnosis.