Accurate diagnosis of MPS I/MPS II can be challenging, particularly in patients with attenuated forms of disease.
Lack of disease awareness, non-specificity of symptoms and a heterogeneous clinical presentation within and between MPS subtypes all contribute to the difficulty in diagnosing MPS I/MPS II.1
A diagnosis algorithm (see below) based on joint symptoms can aid the accurate diagnosis of MPS I/MPS II. Joint contractures are an early manifestation of MPS I and MPS II and are often the initial reason for seeking medical attention in children with attenuated disease.2,3 Natural history data from the global MPS I Registry and Hunter Outcome Survey shows that 57.3-69.3% of individuals with attenuated forms of MPS I and up to 84% of individuals with MPS II have joint contractures.4,5 Joint contractures are not as common in severe forms of MPS I, occurring in 37.9% of patients.4
Joint contractures in individuals with MPS I/MPS II resemble rheumatic conditions and are therefore at risk of being misdiagnosed. However, joint contractures in MPS I/MPS II have several distinguishing features, in particular the absence of systemic and local signs of inflammation (See Clinical presentation).6 Therefore joint contractures without inflammation should always raise suspicion of an MPS disorder.2
Diagnosis algorithm for MPS I/MPS II.
Algorithm adapted from Lehman et al., Rheumatology 2011;50:v41-v48 and Cimaz et al., Pediatric Rheumatology 2009, 7:18
When there is clinical suspicion of an MPS disorder, biochemical testing is required to confirm diagnosis and to determine the MPS subtype (See testing).