A novel germline CDH23 variant as a likely cause of an ultra-giant prolactinoma

Giant prolactinomas are defined as pituitary adenomas (PAs) ≥ 4 cm with plasma prolactin level > 1000 ng/ml with no other co-secretory component. The reasons for development of giant prolactinomas are not clear but genetics play an important pathogenic mechanism in some PAs. In this report, we describe a middle-aged woman who incidentally was found to have an infiltrative giant prolactinoma involving the sellar, supra- and parasellar regions and occupying most of the middle fossae of the skull extending all the way to the occipital and upper cervical regions. Anteriorly, it extends to the sphenoid and parasellar sinuses, nasopharynx and nasal cavities. It was initially thought to be a nasopharyngeal cancer but biopsy from a protruding component from the right nostril showed that it was a prolactinoma. Prolactin level after several dilutions was extremely high at 277,500 ng/ml (normal range 3.4–24.1 ng/ml). Surprisingly, her pituitary function evaluation showed only mild central hypothyroidism [(FT4 11.4 pmol/l (normal range 12–22) and TSH 1.9 mU/l (normal range 0.27–4.2)] and hypogonadotropic hypogonadism (E2 47 pmol/l, LH 1.9 u/l, FSH 5.9 u/l). Cosyntropin stimulation test was normal suggesting normal pituitary adrenal axis but insulin-induced hypoglycaemia test was not performed. In retrospect, the patient reported chronic nasal congestion and snoring, headaches on/off and deterioration in her hearing and visual acuity over the last few years. She ascribed these symptoms to sinusitis and advancing age, respectively. Whole exome sequencing revealed a novel variant in CDH23 (NM_022124.6:c.2621C > A, p.Ala874Asp), a gene that has been previously reported to be associated with PAs. The patient was treated with small doses of cabergoline (0.5 mg twice weekly) and reported remarkable improvement in her symptoms. Radiological evaluation confirmed the significant response of this giant prolactinoma to cabergoline.