Examkin

Soru

Zorluk: ZorDiagnostic Workup and Test Sequencing

A 38-year-old woman is evaluated in the clinic for progressive central obesity, severe fatigue, facial plethora, and easy bruising over the past eight months. She has newly diagnosed hypertension and type 2 diabetes mellitus. Physical examination is notable for wide, violaceous abdominal striae and proximal muscle weakness. To definitively evaluate the etiology of this patient's suspected condition, arrange the following diagnostic steps in the most appropriate chronological sequence, progressing from initial screening to definitive pre-surgical localization. Assume the condition is ultimately driven by a functional microadenoma that measures 3 mm on imaging.

  1. 1Perform a 1-mg overnight dexamethasone suppression test
  2. 2Measure baseline plasma adrenocorticotropic hormone (ACTH) concentration
  3. 3Perform an 8-mg high-dose dexamethasone suppression test
  4. 4Obtain a dedicated magnetic resonance imaging (MRI) scan of the pituitary gland
  5. 5Perform bilateral inferior petrosal sinus sampling with corticotropin-releasing hormone (CRH) stimulation

Cevap

The correct sequence progresses from establishing hypercortisolism (1-mg dexamethasone test), to determining ACTH dependence (plasma ACTH), to biochemical localization (8-mg dexamethasone test), to structural imaging (pituitary MRI), and finally to invasive confirmation (inferior petrosal sinus sampling) due to the equivocal size of the lesion.
The correct sequence strictly adheres to the principle of progressing from biochemical confirmation to structural localization. Hypercortisolism must first be established with a screening test (such as the 1-mg dexamethasone suppression test). Once confirmed, checking the plasma ACTH level determines ACTH dependence. For ACTH-dependent hypercortisolism, a high-dose dexamethasone suppression test is used to biochemically localize the source to the pituitary. Only after this biochemical confirmation should structural imaging (MRI) be performed. Because up to 10% of healthy individuals have pituitary incidentalomas, current guidelines state that an MRI showing a lesion smaller than 6 mm is equivocal; therefore, bilateral inferior petrosal sinus sampling is ultimately required to definitively confirm the pituitary as the source of excess ACTH prior to neurosurgery.

Adım Adım Çözüm

1
Establish the presence of endogenous hypercortisolism.
The 1-mg overnight dexamethasone suppression test will show a failure to suppress cortisol.
Before conducting complex localizing tests, true hypercortisolism must be differentiated from physiological states or simple obesity.
2
Differentiate ACTH-dependent from ACTH-independent causes.
Plasma ACTH concentration will be normal or elevated.
This step critically dictates whether the workup should focus on the adrenal glands (ACTH-independent) or the pituitary/ectopic tissues (ACTH-dependent).
3
Biochemically differentiate pituitary from ectopic ACTH sources.
The 8-mg high-dose dexamethasone suppression test will show suppression of cortisol levels.
Pituitary adenomas typically retain some negative feedback response to high-dose glucocorticoids, whereas ectopic ACTH-secreting tumors usually do not.
4
Structurally localize the suspected pituitary adenoma.
A 3-mm microadenoma is visualized on the MRI.
Imaging is necessary for surgical planning once the biochemical source is confidently localized to the sella turcica.
5
Confirm the pituitary source using invasive venous sampling.
A central-to-peripheral ACTH gradient > 3 after CRH stimulation confirms Cushing disease.
Up to 10% of the healthy population has a pituitary incidentaloma. An MRI showing a lesion < 6 mm is considered equivocal, and IPSS is required to definitively distinguish true Cushing disease from ectopic ACTH syndrome with a coexisting incidentaloma.

Anahtar Kavram

The diagnostic algorithm for Cushing syndrome strictly follows a sequence: confirm hypercortisolism, establish ACTH dependence, biochemically localize the source, perform structural imaging, and utilize inferior petrosal sinus sampling if imaging reveals an equivocal (< 6 mm) lesion.
Tahmini Süre:2m 0s
Bu soruyu puanla

Konular

Diagnostic Workup and Test Sequencing

Bu konudan daha fazla soru