Case Series Analysis of Five Rare Cases of Hyperprolactinemia in Diabetes Mellitus: Clinical Characteristics, Molecular Pathways, and Implications for Targeted Management

Background: Hyperprolactinemia, characterized by serum prolactin levels >20 ng/mL, is a rare comorbidity in diabetes mellitus, potentially exacerbating insulin resistance and glycemic dysregulation via JAK/STAT signaling. This case series analysis examines five rare cases to elucidate clinical patterns, molecular mechanisms, and therapeutic outcomes, aiming to inform precision endocrine management. Methods: Five cases were curated from PubMed and Scopus (1999–2025), focusing on hyperprolactinemia in diabetes (type 1, type 2, or insipidus). Data on demographics, symptoms, laboratory findings (prolactin, insulin, C-peptide), imaging (MRI), and treatment outcomes were extracted. Results: The cohort included 3 females and 2 males (mean age: 26.2 years, range: 7–33). Prolactin levels ranged from 145–3,177 ng/mL, with 2/5 cases (40%) having type 1 diabetes, 1/5 (20%) type 2, 1/5 (20%) diabetes insipidus, and 1/5 (20%) factitious hypoglycemia. Presentations included hypogonadism (3/5, 60%), galactorrhea (2/5, 40%), and hypoglycemia (2/5, 40%). MRI revealed microadenomas (2/5, 40%), a macroadenoma (1/5, 20%), or normal pituitary (2/5, 40%). Cabergoline or medication withdrawal normalized prolactin in 4/5 (80%), reducing levels (e.g., 3,177 to 321 ng/mL in one case) and improving glycemic control (fewer hypoglycemic episodes) in 3/5 (60%). Prolactin activates JAK2/STAT5, inducing SOCS3 to inhibit IRS-1/PI3K/Akt, impairing glucose uptake. Conclusion: Hyperprolactinemia, whether tumoral or non-tumoral, disrupts metabolic homeostasis in diabetes. Routine prolactin screening is recommended for patients with reproductive or glycemic anomalies, emphasizing targeted therapies like dopamine agonists to optimize outcomes.