Nerve growth factor (NGF), which is a neurotrophic factor, is involved in autoimmune and inflammatory processes. Serum NGF levels were investigated in 131 patients with autoimmune (95 with Graves’ disease, of whom 57 had ophthalmopathy, 19 with Hashimoto's thyroiditis) and nonimmune thyroid diseases (17 with toxic nodular goitre), and 20 controls. NGF levels were measured via enzyme-linked immunosorbent assay. Twenty-nine positive cases for NGF were detected: 21 cases in Graves’ disease, 7 cases in Hashimoto's thyroiditis, no case in toxic nodular goitre and one case in controls. NGF levels were higher in patients with Graves’ disease and particularly with Hashimoto's thyroiditis compared with controls (1786.47 ± 34.79 pg/ml and 1996.27 ± 77.71 pg/ml vs 1579.16 ± 57.45 pg/ml, P < 0.049 and P < 0.0001, respectively). Increased NGF levels associated with Graves’ hyperthyroidism and correlated with FT3 (P < 0.01). Patients with the presence of antibodies against TSH receptor showed higher NGF levels than those with no antibodies (1938.61 ± 56.44 pg/ml vs 1712.12 ± 54.22 pg/ml, P < 0.009). Decreased NGF levels were demonstrated in hyperthyroid Graves’ ophthalmopathy compared with those without eye symptoms (1746.65 ± 51.98 pg/ml vs 1910.47 ± 55.62 pg/ml, P < 0.036).
NGF may be involved in the pathomechanism of autoimmune thyroid diseases. Decreased NGF levels in hyperthyroid Graves’ ophthalmopathy highlight the importance of NGF in the neuroprotection of orbital tissues.