The pseudo-Cushing syndrome occurs in some disorders where some but not all of the features of Cushing's syndrome are identified. A number of laboratory tests can aid in the distinction between these 2 conditions.
Features of pseudo-Cushing syndrome:
(1) overproduction of serum cortisol secondary to increased release of ACTH, with elevated 24 hour urine cortisol excretion
(2) some clinical features of Cushing's syndrome
(3) reversal on correction of underlying condition
Conditions associated with the pseudo-Cushing syndrome:
(1) alcohol abuse (including alcohol withdrawal)
(2) depression
(3) obesity
(4) poorly controlled diabetes mellitus
Laboratory tests that can help in the differential diagnosis:
(1) highly sensitive serum PSA
(2) serum testosterone
(3) peak ACTH production after administration of 10 micrograms IV of DDAVP (desmopressin test)
(4) single midnight serum cortisol test
|
Test |
probably pseudo-Cushing |
indeterminate |
Cushing's |
|
serum PSA |
<= 5 pg/mL |
|
> 5 pg/mL |
|
serum testosterone |
< 3 mmol/L |
3 - 3.7 mmol/L |
>= 3.8 mmol/L |
|
ACTH after desmopressin |
< 6 pmol/L |
6 - 12.5 pmol/L |
> 12.5 pmol/L |
|
midnight cortisol |
< 5 µg/dL |
5 - 7.5 µg/dL |
> 7.5 µg/dL |
where:
• A small percentage of patient's with Cushing's syndrome will have test results similar to those seen in pseudo-Cushing's syndrome.
• The serum cortisol was measured by either RIA or fluorescent polarization immunoassay (Abbott Laboratories).
• The serum PSA reference range is <= 5 pg /mL (Figure 1, Coiro et al, page 151).
• The testosterone cutoffs are based on Tables 1 and 2, Coiro et al, page 150.
Limitations:
• The optimum cutoff values for the different tests need to be determined under local conditions before the protocol can be used.
Specialty: Endocrinology, Clinical Laboratory
ICD-10: ,
