Subclinical hypothyroidism, focusing on carpal tunnel syndrome and peroneal neuropathy at the fibular head: a prospective case-control study.

Abstract

Background: Peripheral nerves may be affected in subclinical hypothyroidism (SH).

Objectives: This study aimed to investigate the presence of common entrapment mononeuropathies in patients with SH.

Design and setting: A prospective case-control study conducted between September 2022 and November 2023 at Adana City Training and Research Hospital, Adana, Türkiye.

Methods: SH patients without neurological complaints and healthy individuals over the age of 18 were included. Serum levels of free T3, free T4, thyroid-stimulating hormone (TSH), thyroid peroxidase (TPO) antibody, and creatine kinase (CK) were measured. All participants underwent nerve conduction studies of the upper and lower extremities.

Results: Thirty patients with SH and 40 healthy individuals were included in the study. The percentage reduction in compound muscle action potential (CMAP) amplitude across the knee segment was 2.8 ± 3.5% in healthy individuals and 6.7 ± 6.6% in SH patients (P = 0.017). Apart from this significant difference, other nerve conduction study findings did not differ between the two groups. A positive correlation was observed between CK levels and the percentage reduction in peroneal nerve CMAP amplitude across the knee segment (P = 0.021, r = 0.421). Additionally, there was a positive correlation between TPO antibody levels and F-wave latency in both the median and ulnar nerves (P = 0.028 r = 0.400/P = 0.005 r = 0.501). Electrodiagnostic evaluations revealed carpal tunnel syndrome (CTS) in four patients, peroneal neuropathy at the fibular head (PNFH) in four patients, and ulnar neuropathy at the elbow (UNE) in one patient.

Conclusion: This study suggests that patients with SH may develop subclinical CTS and PNFH, but not UNE. Accordingly, it highlights the importance of avoiding risk factors that may contribute to the development of CTS and PNFH. Serum CK and TPO antibody levels may be useful in monitoring subclinical neuropathy in SH.