Endocrine Abstracts

A 31-year-old engineer presented with a 6-week history of tremor, weight loss, mild goitre and palpitations. At the onset of these symptoms, he also presented to a specialist eye hospital for difficulty with focussing his vision. He had no past medical history and was taking no medications. He did not have any family history of ocular or autoimmune conditions and was a non-smoker. On examination his BMI was 20, he had very mild proptosis, no diplopia and a diffuse symmetrical goitre. His biochemistry confirmed a diagnosis of Graves’ thyrotoxicosis with fT₄ 20.6 pmol/l (9.0–26.0), fT₃ 10.2 pmol/l (2.5–5.7), TSH <0.05 mU/l (0.3–4.2) and positive TSH receptor antibodies 9.7 U/ml (0–0.4). He was commenced on anti-thyroid medications and further definitive management was discussed. Interestingly, it transpired that he was diagnosed with keratoconus of the eye concomitant to the onset of his thyrotoxic symptomatology.

Discussion: Keratoconus is a degenerative disorder in which corneal morphology becomes more conical as a result of stromal thinning. Its aetiology may relate to modifications in corneal collagenases, resulting in breakdown of stromal collagen and is associated with an increased expression of inflammatory mediators in tears. Symptoms include visual distortion or discomfort (often ameliorated by squinting), monocular diplopia or ‘ghosting’ and photosensitivity. The reduced tear production and rubbing of eyes, common in Graves’ disease, is a known precipitant of keratoconus. There is an increased prevalence of keratoconus in immune disorders, including hashimoto’s thyroiditis (OR 2 (CI 1.2–3.3)) (1). In patients with keratoconus the normal thyroxine level in tears has been found to be two orders of magnitude lower than in the serum. Interestingly, independently of their serum thyroid function, patients with keratoconus have tear thyroxine levels 2–50 fold higher than subjects free of ocular pathology (2). Indeed tear thyroxine levels are higher during progression of keratoconus and decline once corneal curvature reaches a new steady value (2).

References

1. Nemet AY, Vinker S, Bahar I & Kaiserman I 2010 The association of keratoconus with immune disorders. Cornea 29 1261–1264.

2. I Kahan, M Varsanyi-Nagy, M Toth, A Nadraj 1990 The possible role of tear fluid thyroxine in keratoconus development. Exp Eye Res 50 339–343.