Information for Orthopedic Surgeons

Because MPS I can affect many different organ systems, patients typically see several specialists before getting a diagnosis. Skeletal and joint manifestations represent the most significant disability and discomfort for patients with MPS I.[2] In severe cases, skeletal involvement in MPS I patients can be detected in the first year of life by radiological methods.[2] Eventually, progressive skeletal dysplasia involving all bones is seen in all patients.

Below are signs and symptoms encountered by orthopedic surgeons that may lead to clinical suspicion of MPS I and warrant further testing.

Carpal tunnel syndrome

Some patients with MPS I may have poor hand function, in part as a result of carpal tunnel syndrome (median nerve entrapment).[2] This syndrome is due to pressure on the median nerve as a result of thickened ligaments within the wrist; it may cause pain, and loss of feeling in the fingertips, but most patients lack these typical symptoms (pain, tingling, or numbness).[3],[4],[5] Because of the high incidence of the syndrome, routine electromyographic/nerve conduction velocity testing is typically recommended by the treating physician, even in the absence of patient complaints.[5]

Carpal TunnelCredit: Illustration courtesy of the National MPS Society

Genu valgum

Many children with MPS I develop genu valgum (knock-knees) severe enough to require surgery.The indication for surgery is a knee deformity greater than 15°.[1] In children too small for staple placement, osteotomies in the large bones around the knee may be required.

Gibbus deformity

Gibbus deformity refers to a bump in the lower back due to an abnormal curvature of the spine. This forward bend, or thoracolumbar kyphosis, in the lower spine occurs in about 90% of children with severe MPS I. It develops from poor bone growth in the upper front part of the vertebrae, which results in a wedging of the vertebrae. Occasionally, children may suffer from both kyphosis and scoliosis, making surgical intervention more likely and more complex. Gibbus deformity is usually observed within 10-14 months.

Gibbus DeformityCredit: Courtesy of E. Kakkis, MD

Spinal cord compression

Progressive compression of the spinal cord with resulting cervical myelopathy due to thickening of the dura (hypertrophic pachymeningitis cervicalis) is common in attenuated MPS I and patients may present initially with reduced activities and exercise tolerance. This complication may not be recognized until it has progressed to the point of irreversible injury.[6]

Spinal Cord CompressionCredit: Illustration courtesy of the National MPS Society

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  1. National MPS Society. Available at: Accessed April 11th, 2017.
  2. Clarke, L.A. Clinical diagnosis of lysosomal storage diseases. In: Organelle Diseases: Clinical Features, Diagnosis, Pathogenesis and Management. Applegarth, D.A., Dimmick, J.E., and Hall, J.G. eds. London: Chapman and Hall Medical; 1997; 46.
  3. Wraith, J.E., and Alani S.M. Carpal tunnel syndrome in the mucopolysaccharidoses and related disorders. Arch Dis Child. 1990; 65:962-963.
  4. Haddad, F.S., Jones, D.H., Vellodi, A., Kane, N., and Pitt, M.C. (1997) Carpal tunnel syndrome in the mucopolysaccharidoses and the mucolipidoses. J Bone Joint Surg Br. 1997; 79:578.
  5. Van Heest, A.E., House J., Krivit, W., and Walker, K. Surgical treatment of carpal tunnel syndrome and trigger digits in children with mucopolysaccharide storage disorders. J Hand Surg Am. 1998; 23:239-241.
  6. Neufeld EF, Muenzer J. The Mucopolysaccharidoses. In: Valle D, Beaudet AL, Vogelstein B, Kinzler KW, Antonarakis SE, Ballabio A, Gibson K, Mitchell G. eds. The Online Metabolic and Molecular Bases of Inherited Disease New York, NY: McGraw-Hill; 2014.§ionid=62642135. Accessed April 11, 2017.
  7. Myer, C.M.D. Airway obstruction in Hurler's syndrome - Radiographic features. Int J Pediatr Otorhinolaryngol. 1990;22:92-95.
  8. Peters, M.E., Arya, S., Langer, L.O., Gilbert, E.F., Carlson, R., and Adkins, W. Narrow trachea in mucopolysaccharidoses. Pediatr Radiol. 1985; 15:226-227.
  9. Stone DL, Sidransky E. Hydrops fetalis: lysosomal storage disorders in extremis. Adv Pediatric. 1999;46:409-440.