title: Primary Hypothyroidism with Exceptionally High Prolactin-A Really Big Deal.
abstract: BACKGROUND
  Primary hypothyroidism can cause both hyperprolactinemia and pituitary hyperplasia. The degree of hyperprolactinemia is generally modest, and rarely do prolactin concentrations exceed 100 ng/mL (4.34 nmol/L). This combination of hyperprolactinemia and pituitary gland enlargement might raise suspicion for a prolactinoma or a nonfunctioning adenoma limiting the ability of hypothalamic dopamine to inhibit prolactin production, the so-called "stalk effect."
  
  
  METHODS
  We describe a 30-year-old female with headaches, galactorrhea, and hyperprolactinemia with a presumptive diagnosis of a prolactinoma. She had hypothyroidism after treatment of Graves disease at age 17 years but was noncompliant with levothyroxine replacement. Thyroid-stimulating hormone (TSH) was 263 mIU/L, FT4 was 3.01 pmol/L, and prolactin was 323 ng/mL (14.06 nmol/L). Magnetic resonance imaging (MRI) demonstrated increased volume of the pituitary gland with homogeneous enhancement with gadolinium. Levothyroxine treatment for 2 weeks decreased her TSH to130 mIU/L, but her total prolactin remained elevated at 386 ng/mL (16.78 nmol/L). Further testing identified that 76% of the total prolactin was macroprolactin.
  
  
  CONCLUSIONS
  Primary hypothyroidism can cause hyperprolactinemia, and prolonged disease may lead to pituitary hyperplasia. However, a marked elevation of prolactin should raise suspicion to investigate additional etiologies for hyperprolactinemia. Our case exemplifies a dual etiology for hyperprolactinemia and pituitary hyperplasia caused by both hypothyroidism and macroprolactin. This knowledge is invaluable for clinicians to avoid unnecessary management with dopamine agonists and/or surgery. This patient's prolactin was 323 ng/mL (14.06 nmol/L). Before our case, the highest prolactin in a hypothyroid patient reported in the literature was 253 ng/mL (11.0 nmol/L).
authors.affiliation: Section of Endocrinology and Metabolism, Department of Medicine, Louisiana State University Health Sciences Center, Shreveport, Louisiana, USA.
authors.forename: Rahim
authors.initials: R
authors.lastname: Khorassanizadeh
authors.affiliation: Section of Endocrinology and Metabolism, Department of Medicine, Louisiana State University Health Sciences Center, Shreveport, Louisiana, USA; Division of Endocrinology, Metabolism, and Diabetes, Department of Medicine, University of Utah School of Medicine, Salt Lake City, Utah, USA.
authors.forename: Vishnu
authors.initials: V
authors.lastname: Sundaresh
authors.affiliation: Section of Endocrinology and Metabolism, Department of Medicine, Louisiana State University Health Sciences Center, Shreveport, Louisiana, USA. Electronic address: slevin@lsuhsc.edu.
authors.forename: Steven N
authors.initials: SN
authors.lastname: Levine
mesh_terms: D000328:Adult; D001921:Brain / Q000000981:diagnostic imaging; D005260:Female; D006801:Humans; D006966:Hyperprolactinemia / Q000000981:diagnostic imaging / Q000209:etiology*; D007037:Hypothyroidism / Q000000981:diagnostic imaging / Q000378:metabolism*; D008279:Magnetic Resonance Imaging; D010902:Pituitary Gland / Q000000981:diagnostic imaging
keywords: Hyperprolactinemia; Hypothyroidism; Macroprolactin; Pituitary adenoma; Pituitary hyperplasia; Prolactin