Differential Diagnosis for High Prolactin and Normal LH
Single Most Likely Diagnosis
- Prolactinoma: This is the most common cause of high prolactin levels. Prolactinomas are benign tumors of the pituitary gland that secrete prolactin, leading to elevated levels. Normal LH levels suggest that the pituitary gland's function is otherwise intact, which is consistent with a prolactinoma.
Other Likely Diagnoses
- Hypothyroidism: High levels of thyroid-releasing hormone (TRH) can stimulate the secretion of prolactin. Hypothyroidism can lead to increased TRH, resulting in elevated prolactin levels. Normal LH levels do not rule out hypothyroidism.
- Pituitary Stalk Interruption: Any lesion or condition that interrupts the pituitary stalk can lead to increased prolactin levels due to the loss of dopamine's inhibitory effect on prolactin secretion. Normal LH levels are possible if the interruption does not significantly affect the secretion of other pituitary hormones.
- Medications: Certain medications, such as antipsychotics, metoclopramide, and some antidepressants, can cause elevated prolactin levels as a side effect. Normal LH levels would be expected unless the medication has other effects on the pituitary gland.
Do Not Miss Diagnoses
- Cranial Lesions: Although less likely, other cranial lesions (e.g., meningiomas, craniopharyngiomas) near the pituitary gland can cause elevated prolactin levels by compressing the pituitary stalk or interfering with dopamine delivery. Missing these diagnoses could lead to significant morbidity or mortality due to tumor growth and potential effects on surrounding brain structures.
- Lymphocytic Hypophysitis: An autoimmune condition that can cause inflammation of the pituitary gland, leading to elevated prolactin levels. It is crucial not to miss this diagnosis due to its potential for significant morbidity if left untreated.
Rare Diagnoses
- Familial Hyperprolactinemia: A rare genetic condition that leads to elevated prolactin levels without any identifiable pituitary tumor or other cause.
- Ectopic Prolactin-Producing Tumors: Rare tumors outside the pituitary gland that can produce prolactin, such as certain lung, breast, or kidney tumors. These are uncommon causes of hyperprolactinemia but should be considered in the appropriate clinical context.