Endocrine Abstracts

Case history : Dopamine agonists are effective and safe first line therapy for prolactinomas. We report an intriguing effect of dopamine agonist therapy in a 68-year-old man commenced on cabergoline treatment for a macroprolactinoma. At review, he reported new nail growth on the tip of a previously partially amputated finger which had been devoid of a fingernail for over four decades. This patient was incidentally diagnosed with a pituitary tumour on a CT brain scan performed for acute delirium during an admission with pneumonia.

Investigations: This was later confirmed on a contrast-enhanced pituitary MRI scan as a 1.9 cm × 1.9 cm × 1.6 cm adenoma extending to the left cavernous sinus and inferiorly to the sphenoid sinus. Pituitary profile showed prolactin of >21,200 mIU/l (63-262), testosterone level low at 6.2 nmol/l (6.51-23.74); other anterior pituitary hormones were normal. He had no symptoms of hyperprolactinaemia, or visual compromise.

Results and treatment: Cabergoline was initiated at a dose of 0.25 mg once weekly after explaining the side effects, increased to twice weekly. He was subsequently seen in out-patient clinic, where he reported no new concerns. To his delight, he had noticed new nail growing on a fingertip that had lost nail following an accident several decades ago. He confirmed that facial hair was growing thicker and faster. The testosterone had normalised to 11.1 nmol/l. The prolactin improved to 18,587 mIU/l, and to 13,409 mIU/l with further dose increase, anticipating further reductions with dose titration.

Conclusion and discussion: Cabergoline, a synthetic ergot derivative, exerts potent and selective inhibition on prolactin secretion by targeting dopamine receptors within pituitary lactotroph cells. Nail growth is dependent on vascular supply. Endothelium-derived relaxing factor plays a key role in blood supply, predominantly endothelial nitric oxide (eNOS). eNOS is inhibited by prolactin; stimulated by oestrogen. Furthermore, keratinocytes essential for nail growth are thought to be activated by oestrogen. Prolactin reduction and consequent reversal of hypogonadism appears to have caused this serendipitous new nail growth in the inactive nail bed of an amputated finger after several decades. The authors propose that the higher testosterone resulting from prolactin suppression by cabergoline led to increased oestrogen by aromatisation, which could account for this phenomenon. To our knowledge, there are no case reports of dopamine agonists stimulating nail growth. There is a case of levodopa-induced nail growth published over 50 years ago, describing accelerated nail growth during Parkinson’s disease treatment. We will monitor this fascinating development with recent dose increments of Cabergoline.