Primary Hypothyroidism with Exceptionally High Prolactin-A Really Big Deal

Area of Science:

• Endocrinology
• Neuroendocrinology
• Pituitary Disorders

Background:

• Primary hypothyroidism is a known cause of hyperprolactinemia and pituitary hyperplasia.
• Elevated prolactin levels in hypothyroidism are typically modest, rarely exceeding 100 ng/mL.
• This presentation can be mistaken for a prolactinoma due to the
• stalk effect.

Observation:

• A 30-year-old female presented with headaches, galactorrhea, and hyperprolactinemia.
• She had severe hypothyroidism (TSH 263 mIU/L, FT4 3.01 pmol/L) and markedly elevated prolactin (323 ng/mL).
• MRI revealed pituitary hyperplasia; treatment for hypothyroidism partially reduced TSH but prolactin remained high, with 76% identified as macroprolactin.

Findings:

• The patient's hyperprolactinemia was attributed to a dual etiology: severe primary hypothyroidism and macroprolactinemia.
• This case presents a prolactin level significantly higher than previously reported in hypothyroid patients.

Implications:

• Distinguishing between hypothyroidism-induced hyperprolactinemia and prolactinoma is critical for appropriate patient management.
• Recognizing macroprolactin as a contributor can prevent unnecessary interventions like dopamine agonist therapy or surgery.
• This case underscores the importance of comprehensive evaluation for hyperprolactinemia, especially in the presence of underlying endocrine disorders.