What Is Cyclical Cushing Disease and How Is It Diagnosed?

Cyclical Cushing disease (a specific form of cyclical Cushing syndrome) is a rare condition where a pituitary tumor releases adrenocorticotropic hormone (ACTH) in unpredictable spurts rather than a more sustained manner. This episodic release causes the body to produce excess cortisol in cycles—with active “high” phases alternating with periods of normal or even low cortisol ^[1][2].

Living with fluctuating symptoms and repeatedly getting contradictory lab results can be emotionally exhausting. This cyclical pattern explains why you might experience worsening symptoms (like weakness, weight changes, or high blood pressure) during peaks and improvements during troughs ^[3]. It also makes diagnosis extremely difficult. Standard lab tests taken during a “low” phase can appear perfectly normal, which can be falsely reassuring and lead to multi-year delays in diagnosis ^[1][3].

Why Cyclical Cushing’s Causes Diagnostic Delays

In typical Cushing disease, cortisol excess is generally more sustained, and the loss of the normal day-night cortisol pattern is more consistent. In cyclical Cushing’s, the unpredictable cycle duration and frequency mean that the disease can effectively “hide” from routine screening ^[1].

Patients often have normal test results when tested during a trough (a low phase) ^[1]. Because symptoms can sometimes spontaneously improve when cortisol levels drop, a normal result obtained during a trough can be falsely reassuring and cause clinicians to suspect other conditions ^[3]. The mismatch between the timing of lab tests and the active phases of the tumor is a primary reason for prolonged diagnostic and treatment delays ^[3][4].

The Diagnostic Process: Why Serial Testing is Needed

Because a single normal test does not rule out cyclical Cushing’s, endocrinologists rely on serial testing over weeks or months. There is no simple number of normal tests that completely rules out the condition; instead, clinicians look for repeated, objectively documented episodes of high cortisol separated by normal or low results ^[1].

Diagnostic strategies often include a combination of the following:

• Serial Late-Night Salivary Cortisol (LNSC): You collect saliva at home late at night. Repeated testing helps detect cyclical cortisol production ^[5][6]. However, strict collection conditions are necessary, as sleep schedules, smoking, bleeding gums, or certain medications can cause false results ^[7].
• Serial 24-Hour Urinary Free Cortisol (UFC): Repeated urine collections help capture periods of excess cortisol ^[6]. Each 24-hour collection must be complete, and results are interpreted alongside your kidney function ^[3]. Multiple normal results between high periods are expected.
• 1-mg Dexamethasone Suppression Test (DST): A screening test where you take a steroid pill (dexamethasone) at night and have your blood drawn the next morning to see if your body appropriately suppresses cortisol production ^[8]. In cyclical Cushing’s, this test can sometimes yield contradictory results depending on the phase ^[9].
• Symptom Tracking: While symptoms do not always align perfectly with biochemical peaks, tracking your symptoms (like rapid weight gain, severe weakness, or high blood pressure) provides helpful context. It can help your endocrinologist plan clinician-directed serial testing to increase the chances of catching an active phase ^[3].
• Hair Cortisol Testing: Segmental scalp-hair analysis measures cortisol deposited in the hair shaft over time. While it cannot reliably confirm or exclude cyclical disease on its own, it can provide complementary clues about longer-term patterns of cortisol exposure ^[10][11]. Results can be affected by hair treatments, washing frequency, and individual hair growth rates ^[12].

Locating the Source: BIPSS

Once active, ACTH-dependent hypercortisolism is biochemically confirmed, an invasive specialized procedure called bilateral inferior petrosal sinus sampling (BIPSS) may be used. BIPSS helps distinguish a pituitary tumor from an ectopic (non-pituitary) ACTH source. It is not a routine screening test, carries procedural risks, and must be performed during a documented active “high” phase; if done during a trough, it can produce misleading results that obscure the true source ^[1][13].

Important Safety and Medication Note

Always tell your doctor about any oral, injected, inhaled, topical, or supplemental steroids you take, as these can alter test results and mimic or mask Cushing’s ^[14].

When to Seek Urgent Care: Do not wait for your next planned test if you experience severe symptoms. Seek prompt medical care for chest pain, shortness of breath, fainting, confusion, severe or rapidly worsening weakness, very high blood pressure, or signs of serious infection ^[15].