Hurler\'s syndrome (mucopolysaccharidosis type I-H): Characteristic skeletal abnormalities

Clinical History

A four-year-old boy presented with walking difficulties, and he had a history of a storage disease.

Imaging Findings

A four-year-old boy presented with walking difficulties, and he had previously been diagnosed with Hurler's syndrome. He had been treated twice with bone marrow transplantation. MRI imaging of the brain, the spine and the hips was performed to evaluate his motor problems. The MRI of the brain showed normal myelination and gyration. At the craniocervical junction, there was hypoplasia of the dens with a slight anterior subluxation of C1 on C2. There was an increased soft tissue posterior to the dens and a narrowing of the spinal canal at the C1 level. There was no signal change within the cord to indicate compression at that level. An MRI of thoracolumbar spine revealed vertebral bodies that were generally reduced in height. There was kyphosis centred at T1, causing a narrowing of the spinal canal and a gibbus at the lumbosacral junction centred on L1 with no cord compression. The MRI of the pelvis revealed up sloping acetabulae, coxa valga and wide femoral necks. The signals from the epiphyses were found to be normal. The findings of the skeleton were typical of Hurler’s syndrome.

Discussion

Mucopolysaccharidoses (MPSs) are a group of storage diseases, produced by an inherited deficiency of a lysosomal enzyme necessary for the degradation of glycosaminoglycans (GAG). Hurler's syndrome is an autosomal recessive disease. The activity of the enzyme alpha-L-iduronidase is decreased, with a consequent accumulation of mucopolysaccharides (dermatan sulphate and heparan sulphate) in the lysosomes of the cells in the connective tissue. The incidence of the disease is 1:100,000 and equally affects males and females. The age of detectability is 12–24 months, and the patients die from cardiopulmonary complications by the age of 5–10 years. The diagnosis is based on the clinical picture, radiological findings, and laboratory results. The main clinical features of the disease are dwarfism, progressive mental deterioration, a large head with coarse features and thoracolumbar kyphosis. Other findings include hepatosplenomegaly and cardiovascular involvement. Radiological findings are characterized by the failure of endochondral ossification and the development of osteoarthritic changes, particularly noticeable in the hips. There is dolichocephaly, frontal bossing, delayed closure of the fontanelles, and a large J-shaped sella with a deepening of the optic chiasm and platybasia. The facial bones are small with narrow nasal passages and an obtuse mandibular angle. An MRI of the brain may demonstrate multicystic non-enhancing changes involving the periventricular white matter. These changes correspond to the accumulation of glycosaminoglycans at the Virchow–Robin spaces and can lead to brain atrophy. A significant characteristic is odontoid dysplasia, with an increased risk of atlantoaxial subluxation and potential cervical spinal cord injury. MR imaging of the cervical spine may demonstrate the presence of an abnormal dural soft-tissue mass at the C2 level, ligamentous thickening and canal stenosis. There is also thoracolumbar kyphosis with lumbar gibbus, due to wedge-shaped vertebral deformities (anterior beak of the lower third of the body). The chest X-ray scan usually demonstrates heart enlargement. There are also small scapulae with flat glenoid cavities, short and thick clavicles and a spatulate configurat ion of the ribs. Radiological findings of the pelvis consist of widely flared iliac wings, and hypoplastic ischial bones with possible hip subluxation or dislocation. Coxa valga is another common finding. There is shortening, enlargement and bowing of the diaphyses of the long bones with minimal metaphyseal or epiphyseal involvement producing the so-called “baton-like appearance”. Forearm bones are enlarged (the radius being longer than the ulna), with the distal articular surfaces facing one another. Delayed maturation of the carpal bones, and claw hands with short, squat metacarpals may also be seen. Progressive deposition of glycosaminoglycan within the myointima of the coronary arteries and airways leads to cardiac and respiratory failure. Subsequently, patients usually die within the first decade of life. Bone marrow transplantation (BMT) was first reported in 1981 as a means of reversing the subsequent lethal course of the disease, by providing a lasting source of leucocytes. Subsequently, they migrate throughout the body and produce a biologically active enzyme which degrades the accumulated lethal GAG deposits. More recently, it has also been shown that successful engraftment after BMT has had beneficial effects on the long-term follow-up of the heart in patients with Hurler's syndrome.

Differential Diagnosis List

Final Diagnosis

Hurler's syndrome.

URL:	https://eurorad.org/case/3161
DOI:	10.1594/EURORAD/CASE.3161
ISSN:	1563-4086