Osteoporosis - A Disappearing Manifestation of Cushing's Syndrome.
E Searle1, K Darzy1, J Adams2 & SM Shalet1
Osteoporosis is considered to be a cardinal feature of Cushing's syndrome with a reported incidence as high as 90%. We conducted a cross-sectional analysis of baseline bone mineral density (BMD) in 21 patients (4 males) aged 19-63 (median, 37) years with untreated Cushing's syndrome. 18 patients had pituitary dependent disease and 3 adrenal adenomas. Dual energy x-ray absorptiometry (DEXA) was used to measure the BMD at the lumbar spine (L1-L4), left femoral neck (LFN) and total left hip (TLH) with single energy x-ray absorptiometry (SXA) used for the wrist (distal and ultradistal sites).
The z-scores (mean ± SD) of the 21 patients were significantly reduced (compared with normal population; mean Z-score = 0) at the lumbar spine (-0.826 ± 1.16; p < 0.001) and the LFN (-0.889 ± 0.884; p < 0.001), while the Z-scores at TLH (-0.162 ± 0.606), distal (-0.680 ± 1.19) and ultradistal (0.278 ± 1.25) sites were not significantly different from normal (p > 0.05).
T-scores (bone mass compared to a reference group of young healthy individuals) were available in 15 patients, none of whom had osteoporosis (T-score <-2.5; WHO criteria) at the lumbar spine; nine being osteopenic (T-score between -1 and -2.5) and 6 normal (T-score >-1). Similarly at the left femoral neck only one patient was osteoporotic; ten osteopenic and four normal. No patient had a history of low trauma fractures.
In terms of the relationship between the severity of the Cushing's syndrome and skeletal health, the only significant finding was a moderate negative correlation between the lumbar spine Z-score and the mean 24hr urinary free cortisol (r = -0.51; p < 0.05).
In conclusion, the textbooks are in need of revision as osteoporosis is no longer a common feature of Cushing's syndrome. In the modern era, earlier diagnosis as well as the detection of disease of milder intensity has changed the skeletal contribution to the clinical presentation of Cushing's syndrome.