Interpreting IGF-1 in TBI Patients: The Overlooked Influence of Liver Disease

Case Diagnosis: A patient with a mild traumatic brain injury (mTBI) presents with persistent fatigue and brain fog, with low IGF-1 levels attributed to liver fibrosis rather than growth hormone deficiency.

Case Description or Program Description: A 41-year-old female sustained an mTBI with loss of consciousness after striking her head on a countertop, with 6-months of persistent brain fog following the injury prompting endocrinological evaluation for possible growth hormone deficiency (GHD), a common consequence of TBI. Initial testing revealed significantly low Insulin-like Growth Factor-1 (IGF-1) levels: 10 ng/mL (reference range: 52-328 ng/mL), with a corresponding z-score of -4.4, suggesting possible GHD. Despite these findings, glucagon stimulation testing demonstrated a peak growth hormone level of 5 ng/mL (reference: ≥3 ng/mL ), ruling out growth hormone deficiency. The remaining neuroendocrine labs and liver enzymes were all normal.

Further diagnostic evaluation with ultrasound elastography revealed underlying liver fibrosis, which can impair the liver’s ability to produce IGF-1. The observed low IGF-1 levels, despite normal growth hormone function, can be explained by liver disease. The liver’s role in IGF-1 production underscores the importance of considering liver health when interpreting IGF-1 results, given the limited sensitivity and specificity of IGF-1 as a standalone marker for GHD.

Setting: Quanternary Care Outpatient Clinic

Assessment/Results: The patient’s symptoms were attributed to her post-TBI state and underlying liver disease rather than endocrine dysfunction. Despite normal growth hormone function, liver dysfunction led to artificially low IGF-1 levels.

Discussion (relevance): This case highlights the complexities of diagnosing endocrine disorders post-TBI. It emphasizes considering alternative confounders in the differential diagnosis for low IGF-1, as factors like liver disease can also cause low levels, aside from GHD.

Conclusions: Clinicians should consider alternative causes of low IGF-1 levels, given the broad differential diagnosis, in patients who have suffered a traumatic brain injury. A holistic diagnostic approach is essential to ensure accurate interpretation and effective management.