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Introduction: Small fiber neuropathies (SFN) are associated with a reduction in quality of life. In adults, epidermal nerve fiber density (END) analysis is recommended for the diagnosis of SFN. In children, END assessment is not often performed. We analyzed small nerve fiber innervation to elucidate the potential diagnostic role of skin biopsies in young patients with pain.Methods: Epidermal nerve fiber density and sudomotor neurite density (SND) were assessed in skin biopsies from 26 patients aged 7 to 20 years (15 female patients) with unexplained chronic pain. The results were compared with clinical data.Results: Epidermal nerve fiber density was abnormal in 50% and borderline in 35% of patients. An underlying medical condition was found in 42% of patients, including metabolic, autoimmune, and genetic disorders.Discussion: Reduction of epidermal nerve fibers can be associated with treatable conditions. Therefore, the analysis of END in children with pain may help to uncover a possible cause and guide potential treatment options. [ABSTRACT FROM AUTHOR]

• Weakness of the feet dorsiflexors can evolve in IOPD after long-term ERT. • This distal weakness is due to progression of the myopathy. • A neuropathy in IOPD constitutes a further symptom that may evolve despite ERT. Enzyme replacement therapy in infantile onset Pompe disease has led to a new phenotype with features not known in the pre-enzyme replacement therapy era. We investigated the origin of a rapidly emerging and severe weakness of the foot dorsiflexors in a 7-year-old boy after 6.5 years of enzyme replacement therapy. Electroneurography yielded normal findings except low compound muscle action potentials of the extensor digitorum brevis muscles after stimulation of the peroneal nerves. Electromyography of the tibial muscle demonstrated a myopathic pattern. Tibial muscle, sural nerve, and skin biopsy showed a myopathy with empty and glycogen containing vacuoles, a mild loss of myelinated and unmyelinated axons, and a moderately reduced intraepidermal nerve fiber density. These findings provide evidence for a severe distal muscle involvement and a mild sensory neuropathy evolving during the course of disease after long-term enzyme replacement therapy, thereby expanding the new emerging phenotype of infantile onset Pompe disease. [ABSTRACT FROM AUTHOR]