Pituitary Iron: Effect on Pituitary Volume and Function in Transfusion Dependent Thalassemia

The association of iron toxicity with vital organ dysfunction has been extensively investigated in transfusion-dependent-thalassemia (TDT). However, pituitary iron load and its effect on function have been infrequently addressed. Growth delay, hypogonadism and infertility resulting from iron-induced pituitary toxicity are still prevalent, impacting clinical care and patients' quality of life. Early recognition and timely intervention can potentially prevent irreversible damage and restore partial function.

Aims

We aimed to determine pituitary iron load and anterior pituitary volume by MRI in various age groups of TDT and examine their association with systemic and organ-specific iron measures. Additionally, we attempted to stratify the occurrence of abnormal anterior pituitary function by these MRI findings. Identifying such risk thresholds could assist in establishing timing and effectiveness of treatment intervention.

MRI (1.5T) measurements of anterior pituitary iron (R2) and volume (Vol) were compared to normal controls (Noetzli 2011) with resultant Z-scores. Mean annual ferritin was calculated and cardiac and liver iron concentration (LIC) were determined by MRI-T2* and superconducting quantum interference device (SQUID) biosusceptometry, respectively. Pituitary hormones (LH and FSH) and growth hormone (Z scores for IGF-1 and IGF-BP3) were determined.

Results

Fifty-three TDT patients (51% females) age 25±8 years, (range 10-45 years) were enrolled. Thirty-three (62%) had a Z_R2 value >2 (mean 5.4) indicating iron accumulation above 97.5^th percentile. Thirty-two patients (60%) had a Z-score for anterior-volume (Z_VOL) of less than -2 (mean -2.8) indicating gland shrinkage below the 2.5^th percent. In 23 patients (43%) both Z_R2 and Z_VOL exceeded these thresholds. Z_R2 inversely correlated with Z_VOL; r =-0.32, p<0.02. Pituitary iron increased with age and differed between patients <18 yr (n=14) and those 18-45 yr (n=39) with a mean Z_R2 at 0.9±0.6 and 4.3±0.5, respectively (p<0.001). Anterior pituitary volume declined in older patients, lagging after the iron accumulation (Figure).

LH/FSH values and Z_R2 showed inverse correlation: r = -0.27 (p<0.03) and -0.3 (p< 0.006) respectively. Z_VOL and LH/FSH demonstrated a positive correlation: r = 0.40, p<0.05 and 0.37, p<0.003, respectively. Z(IGF-BP3) but not Z(IGF-1) had an inverse correlation with Z_R2: r = -0.5 (p<0.001).

Z_R2 > 4 was found to be a significant predictor for gland shrinkage; Zvol < -2 was present in 17/33 patients with a Z_R2>4 compared to 3/20 with a Z_R2<4 (p<0.009). Receiver operator (ROC) analysis confirmed it with an AUC of 0.68. Z_R2 >4 was also predictive of presence of clinically important cardiac (T2* <20ms, AUC=0.92, p<0.001) and hepatic iron (LIC >10mg/g_d.w., AUC= 0.74, p<0.005). Mean ferritin significantly correlated with Z_R2 (p<0.001) but not with the gland's volume.

Conclusions

Anterior pituitary iron assessed by MRI, increases with age and correlates with total body iron burden in TDT, suggesting cumulative iron toxicity. It results in a decrease in gland size and impaired gonadotropin and growth hormone secretion. Pituitary iron exceeding Z_R2 >4, appears to be a significant predictor for change in gland size, that also is associated with cardiac and liver iron-overload. Pituitary MRI and the concomitant liver and cardiac iron quantification can identify patients at high-risk for further pituitary damage, suggesting that early intervention can potentially prevent additional decline in hormonal secretion.

Figure

View largeDownload slide

Figure

View largeDownload slide

Close modal