124
Test Weight ≥40 Kg Weight ≤40 Kg
ONDST 1 mg at 2300h 15 μg/Kg at 2300h
LDDST 0.5 mg, 6 hourly × 2 days 30 μg/Kg/day in four divided
doses × 2 days
HDDST 2 mg, 6 hourly × 2 days 120 μg/Kg/day in four divided
doses × 2 days- What is the importance of diurnal variation of cortisol secretion in the diagno-
sis of Cushing ’ s syndrome?
Cortisol secretion peaks at 0400–0800h and troughs at 2300–2400h and this
diurnal rhythm is established by 2–3 years of age. Diurnal variation of cortisol
secretion prevents sustained hypercortisolemia, which may be detrimental to
neuronal function and sleep. Loss of diurnal rhythm of cortisol secretion is
defi ned as a 1600h serum cortisol level >50 % of 0800h serum cortisol or 2300h
serum cortisol ≥207 nmol/L. This is the earliest abnormality of hypothalamo–
pituitary–adrenal axis in patients with Cushing’s syndrome. Other causes of
altered diurnal rhythm include pseudo-Cushing syndrome, seizure disorder,
depression, use of anticonvulsants, and shift-workers. However, pregnancy and
glucocorticoid resistance syndrome are associated with preserved diurnal
rhythm of cortisol secretion despite high serum cortisol. - A 13 - year - old female with specifi c features of Cushing ’ s syndrome has 0800h
cortisol 540 nmol / L ( 20 μ g / dl ), normal urine free cortisol , and suppressible
LDDST. Is the diagnosis of Cushing ’ s syndrome excluded?
No. In the index patient with a high clinical suspicion of Cushing’s syndrome,
a normal UFC and a suppressible LDDST does not rule out the diagnosis of
Cushing’s syndrome. A midnight serum cortisol should be performed in this
scenario, as the earliest biochemical abnormality in Cushing’s syndrome is loss
of diurnal rhythm. If sleeping midnight serum cortisol is ≥50 nmol/L (1.8 μg/
dl), a possibility of mild Cushing’s syndrome should be considered. In such
circumstances, patients should be kept under close surveillance with periodic
revaluation of cortisol dynamics. Further, even if the midnight serum cortisol is
normal, a possibility of cyclical Cushing’s syndrome should be kept and serial
monitoring of UFC should be performed. - What is the role of late - night salivary cortisol for the diagnosis of Cushing ’ s
syndrome in children?
Late-night salivary cortisol (LNSC) measures free cortisol and is devoid of
interference from alterations in cortisol-binding globulin. It is a simple nonin-
vasive test and sampling for LNSC can be done even at home. Therefore, it is
one of the fi rst-line screening tests for the diagnosis of Cushing’s syndrome in
adults. However, it is not preferred as a screening test in childhood Cushing’s
syndrome as limited data is available regarding the use of LNSC in children.
4 Childhood Cushing’s Syndrome