Neurophysiological Characteristics of Upper Extremity Neuropathy in Three Young Patients with Mucopolysaccharidosis...

Background/Objectives: To date, few studies have reported the use of neurophysiological testing to assess the long-term progression of functional changes in median and ulnar nerve conduction in children and adolescents with mucopolysaccharidosis (MPS). This case series study aimed to perform an electroneurographic (ENG) assessment of the median and ulnar nerves in three young patients with MPS treated with enzyme replacement therapy (ERT) and hematopoietic stem cell transplantation (HSCT) over a five-year observation period. Methods: Bilateral electroneurography of the motor and sensory fibers in the median and ulnar nerves, recording compound muscle action potential (CMAP) and sensory nerve action potential (SNAP), was performed twice in 5-, 7-, and 19-year-old males at two time points: before and five years after the application of ERT and HSCT. Results: In three MPS patients with Hurler or Hunter syndrome, ENG studies similarly demonstrated decreased amplitudes and prolonged distal latencies in their CMAP recordings, confirming the bilateral progression of axonal degeneration and demyelinating changes in the distal parts of the median nerves. The SNAP recordings revealed more severe degenerative processes of similar types in the sensory fibers of the median nerves. Nerve conduction studies in the ulnar nerve fibers bilaterally revealed analogous pathologies, but with a lesser degree of progression. Conclusions: This study confirms the progression of axonal degeneration and demyelinating changes in the distal parts of the median nerves, which were associated with decreased amplitudes and prolonged distal latencies in the CMAP recordings of the MPS patients. More expressed degeneration processes of a similar type were found in the sensory fibers of the median nerves. Ulnar nerve pathologies of neural conduction are less advanced in patients with Hurler and Hunter syndromes. It seems advisable to implement neurophysiological diagnostics as soon as possible to specify surgical or conservative therapy, which is crucial for maintaining hand function in the case of progressive peripheral neuropathies in patients with MPS. The timing of the treatment and the patient's age may be factors influencing the effectiveness of treatment.