{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,13]],"date-time":"2026-07-13T12:12:12Z","timestamp":1783944732028,"version":"3.55.0"},"reference-count":22,"publisher":"BMJ","issue":"7","content-domain":{"domain":["bmj.com"],"crossmark-restriction":true},"short-container-title":["BMJ Case Rep"],"accepted":{"date-parts":[[2026,7,1]]},"published-print":{"date-parts":[[2026,7]]},"abstract":"<jats:p>We report a woman in her 50s with a giant co-secreting pituitary macroadenoma producing both prolactin and growth hormone. She presented with headache, proptosis, chemosis and secondary amenorrhoea since her 20s. Workup showed hyperprolactinaemia (251 \u03bcg\/L; normal \u226423 \u03bcg\/L). A brain MRI showed a giant mass at the base of the skull. Repeat prolactin assay after serum dilution showed marked hyperprolactinaemia (386\u2009020 \u03bcg\/L), consistent with a giant prolactin-secreting tumour. Additional tests established the presence of growth hormone excess. She was treated with cabergoline, leading to substantial clinical improvement and progressive decrease in tumour size and prolactin. Additionally, she was initially treated with lanreotide which was ineffective. She was switched to pegvisomant therapy, resulting in insulin-like growth factor I normalisation. This case emphasises the critical importance of recognising the hook effect artefact in patients with large sellar masses. Slow uptitration of dopamine agonist therapy is advisable in patients with large tumours to minimise the risks of cerebrospinal fluid leak, apoplexy and herniation.<\/jats:p>","DOI":"10.1136\/bcr-2026-272948","type":"journal-article","created":{"date-parts":[[2026,7,13]],"date-time":"2026-07-13T11:35:24Z","timestamp":1783942524000},"page":"e272948","update-policy":"https:\/\/doi.org\/10.1136\/crossmarkpolicy","source":"Crossref","is-referenced-by-count":0,"title":["Hyperprolactinaemia masked by the hook effect in a patient with a giant prolactinoma with growth hormone co-secretion"],"prefix":"10.1136","volume":"19","author":[{"given":"Ghazal","family":"Daftari","sequence":"first","affiliation":[{"name":"Neuroendocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0005-4640-9519","authenticated-orcid":false,"given":"Risa","family":"Waki","sequence":"additional","affiliation":[{"name":"Neuroendocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, USA"},{"name":"Yokohama City University School of Medicine Graduate School of Medicine, Yokohama, Kanagawa Prefecture, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Deborah A","family":"Forst","sequence":"additional","affiliation":[{"name":"Neurology, Division of Neuro-oncology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Pamela S","family":"Jones","sequence":"additional","affiliation":[{"name":"Neurosurgery, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8867-607X","authenticated-orcid":false,"given":"Nicholas","family":"Tritos","sequence":"additional","affiliation":[{"name":"Neuroendocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"239","published-online":{"date-parts":[[2026,7,13]]},"reference":[{"key":"2026071304351406000_19.7.e272948.1","doi-asserted-by":"publisher","DOI":"10.1056\/NEJMcp0912025"},{"key":"2026071304351406000_19.7.e272948.2","doi-asserted-by":"crossref","first-page":"305","DOI":"10.1016\/j.otc.2021.12.005","article-title":"Prolactinoma: Medical and Surgical Considerations","volume":"55","author":"Haider","year":"2022","journal-title":"Otolaryngol Clin North Am"},{"key":"2026071304351406000_19.7.e272948.3","doi-asserted-by":"crossref","first-page":"104080","DOI":"10.1016\/j.lpm.2021.104080","article-title":"Prolactinomas","volume":"50","author":"Wildemberg","year":"2021","journal-title":"Presse Med"},{"key":"2026071304351406000_19.7.e272948.4","doi-asserted-by":"publisher","DOI":"10.1210\/jc.2010-1692"},{"key":"2026071304351406000_19.7.e272948.5","doi-asserted-by":"publisher","DOI":"10.1038\/s41574-023-00886-5"},{"key":"2026071304351406000_19.7.e272948.6","doi-asserted-by":"crossref","first-page":"296","DOI":"10.4158\/EP.8.4.296","article-title":"\u201cHook effect\u201d in prolactinomas: case report and review of literature","volume":"8","author":"Frieze","year":"2002","journal-title":"Endocr Pract"},{"key":"2026071304351406000_19.7.e272948.7","doi-asserted-by":"crossref","first-page":"1043","DOI":"10.3171\/jns.1998.89.6.1043","article-title":"Excessively high prolactin level in a patient with a nonprolactin-secreting adenoma. 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