In order of decreasing frequency, the following are the most common causes of nipple discharge in the nonlactating breast: duct ectasia, intraductal papilloma, and carcinoma. The important characteristics of the discharge and some other factors to be evaluated by history and physical examination are as follows:

(1) Nature of the discharge (serous, bloody, or other).
(2) Association with a mass.
(3) Unilateral or bilateral.
(4) Single or multiple duct discharge.
(5) Discharge is spontaneous (persistent or intermittent) or must be expressed.
(6) Discharge is produced by pressure at a single site or by general pressure on the breast.
(7) Relation to menses.
(8) Premenopausal or postmenopausal.
(9) Patient is taking contraceptive pills or estrogen.

Unilateral, spontaneous serous or serosanguineous discharge from a single duct is usually caused by an intraductal papilloma or, rarely, by an intraductal cancer. A mass may not be palpable. The involved duct may be identified by pressure at different sites around the nipple at the margin of the areola. Bloody discharge is suggestive of cancer but is more often caused by a benign papilloma in the duct. Cytologic examination may identify malignant cells, but negative findings do not rule out cancer, which is more likely in women over age 50 years. In any case, the involved duct - and a mass if present - should be excised. Ductography is of limited value since excision of the bloody duct system is indicated regardless of findings. Ductoscopy is being evaluated as a means of identifying intraductal lesions but is not yet practical.

In premenopausal women, spontaneous multiple duct discharge, unilateral or bilateral, most marked just before menstruation, is often due to mammary dysplasia. Discharge may be green or brownish. Papillomatosis and ductal ectasia are usually seen on biopsy. If a mass is present, it should be removed.

A milky discharge from multiple ducts in the nonlactating breast occurs in certain endocrine syndromes, as a result of hyperprolactinemia. Serum prolactin levels should be obtained to search for a pituitary tumor. Thyroid-stimulating hormone (TSH) helps exclude causative hypothyroidism. Numerous antipsychotic drugs and other drugs may also cause a milky discharge that ceases on discontinuance of the medication.

Oral contraceptive agents or estrogen replacement therapy may cause clear, serous, or milky discharge from a single duct, but multiple duct discharge is more common. The discharge is more evident just before menstruation and disappears on stopping the medication. If it does not stop and is from a single duct, exploration should be considered.

A purulent discharge may originate in a subareolar abscess and require removal of the abscess and the related lactiferous sinus.

When localization is not possible, no mass is palpable, and the discharge is nonbloody, the patient should be reexamined every 2 or 3 months for a year, and mammography should be done. Although most discharge is from a benign process, patients may find it annoying or disconcerting. To eliminate the discharge, proximal duct excision can be considered both for treatment and diagnosis. Cytologic examination of the nipple discharge for exfoliated cancer cells may rarely be helpful in diagnosis. However, the duct may be catheterized and lavage performed to evaluate cells for atypia. Ductoscopy, evaluation of the ductal system with a small scope inserted through the nipple, is also being studied to help identify intraductal lesions that may be causing the discharge.

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