Prolactinoma is a prolactin-secreting pituitary adenoma and is the most common functioning pituitary tumour. Excess prolactin secretion causes reproductive and endocrine dysfunction by suppressing gonadotropin secretion. Prolactinomas are classified according to tumour size into microprolactinomas and macroprolactinomas. Unlike most pituitary tumours, the first-line treatment for prolactinoma is medical therapy rather than surgery.

Pathophysiology

Prolactinomas arise from lactotroph cells of the anterior pituitary gland, resulting in excessive secretion of prolactin. Elevated prolactin suppresses hypothalamic gonadotropin-releasing hormone (GnRH), leading to reduced luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion, causing hypogonadism, infertility, menstrual disturbances, and sexual dysfunction. Large tumours may also produce symptoms due to compression of surrounding structures, particularly the optic chiasm.

Classification

• Microprolactinoma: Tumour size <10 mm

• Macroprolactinoma: Tumour size >10 mm

Clinical presentation

Symptoms are mainly due to hyperprolactinaemia and may include:

• Galactorrhoea

• Oligomenorrhoea or amenorrhoea

• Infertility

• Reduced libido

• Erectile dysfunction (impotence)

• Gynaecomastia in males

• Headache

• Visual abnormalities, particularly in large adenomas

Diagnostic criteria

Diagnosis is based on serum prolactin levels together with clinical features.

Serum prolactin interpretation:

• <100 ng/mL: Possible prolactinoma

• 100–200 ng/mL: Likely prolactinoma

• >200 ng/mL: Diagnostic of prolactinoma

Investigations

• Serum prolactin level

Management

Pharmacological management

Prolactinomas are unique among pituitary tumours because medical therapy is the first-line treatment, rather than surgery.

The mainstay of treatment is a dopamine agonist:

• Bromocriptine (PO) 2.5–20 mg once daily or in two divided doses.

OR

• Cabergoline (PO) 0.25–1 mg twice weekly.

Prognosis

The prognosis is generally excellent with appropriate treatment. Most patients achieve normalization of prolactin levels, reduction in tumour size, restoration of gonadal function, and improvement in fertility and symptoms. Macroprolactinomas may require longer treatment and close follow-up, particularly if visual impairment or mass effects are present.