Background: We studied involvement of large and small nerve fibres in patients with hypothyroidism and symptoms and signs of polyneuropathy.
Methods: Sixteen patients with established diagnosis of hypothyroidism were extracted from a patient population participating in a 'polyneuropathy study'. In addition, seven patients with other additional potential causes of polyneuropathy than hypothyroidism were investigated. The patients underwent neurological examination, routine blood tests, nerve conduction studies (NCS), quantitative sensory testing (QST) and skin biopsies with assessment of intraepidermal nerve fibre (IENF) density.
Results: Sixty-three per cent of the patients with 'pure' hypothyroidism had abnormalities on NCS, 25% had reduced IENF density and 31% had abnormalities on QST. Four patients (25%) met criteria for small fibre polyneuropathy, the other (75%) were classified as having mixed fibre polyneuropathy. There were no differences in the amount of abnormalities on NCS, QST and skin biopsy between patients with hypothyroidism and those with hypothyroidism and other potential causes of polyneuropathy.
Conclusions: The majority of patients with hypothyroidism had involvement of both large and small nerve fibres. However, some patients had isolated small fibre polyneuropathy. Patients with 'pure' hypothyroidism had essentially the same degree of peripheral nerve fibre involvement as those with other additional causes of polyneuropathy.