SUN-202 Nerve Conduction Studies May Predict the Natural Course of Mild Subclinical Hypothyroidism in Children

Abstract Disclosure: G. Çatlı: None. O. Besci: None. T.Ü. Hale: None. M. Ayanoğlu: None. S.A. Hiz: None. E. Böber: None. A. Abacı: None. U. Yiş: None. Background: There have been conflicting reports on nerve conduction studies (NCS) in adults with subclinical hypothyroidism (SH). However, no study has evaluated nerve conduction and its relationship to thyroid autoimmunity in children with SH. This prospective study evaluates NCS via electroneuromyography (ENMG) in pediatric patients with SH and investigates long-term thyroid function evolution and its association with neuromuscular alterations. Methods: A total of 24 children aged 5-18 years diagnosed with SH underwent baseline ENMG to assess motor and sensory nerve conduction parameters. Following this assessment, the children were monitored for five years to determine disease progression. ENMG results were compared between groups, and associations with thyroid autoimmunity were examined. Results: Motor axonal impairments were detected in 33.3% of patients with SH. The most frequently affected nerve was the peroneal (20.8%), followed by the tibial (8.3%) and ulnar (8.3%) nerves. No sensory involvement was observed. Abnormalities included increased latency in the ulnar (4.2%), tibial (8.3%), and peroneal (8.3%) nerves and decreased amplitude in the ulnar (4.2%) and peroneal (16.7%) nerves. During follow-up, 37.5% of patients developed persistent SH, requiring levothyroxine treatment, while 62.5% experienced spontaneous normalization of thyroid function. Among patients with persistent SH, 77.8% had axonal impairments compared to only 6.7% in the euthyroid group (p=0.001). A significant association was found between axonal involvement and persistent SH, with a relative risk of 7. Patients with persistent SH had significantly prolonged tibial motor nerve conduction latency (4.9 ms [IQR 2.0] vs. 3.8 ms [IQR 1.1], p=0.02). Higher TPOAb levels were observed in patients with axonal involvement compared to those without (p=0.03), and TGAb levels positively correlated with median and tibial nerve latencies (rs=0.607, p=0.002; rs=0.44, p=0.03). Conclusion: This study is the first to assess neuromuscular function in children with SH. A significant association was found between axonal impairment and the development of persistent SH, suggesting that axonal involvement may serve as a marker for identifying patients at higher risk of disease progression. The increased susceptibility of motor nerves in SH may be linked to their myelin structure, metabolic demands, autoimmune processes, and regeneration capacity. In contrast, the preservation of sensory nerves could be attributed to their lower energy requirements and superior regenerative potential. These findings highlight the importance of neuromuscular assessment in predicting thyroid function evolution in pediatric SH. Presentation: Sunday, July 13, 2025