Early Detection of Subclinical Cushing Syndrome: Current Evidence and Clinical Strategies

Abstract

Subclinical Cushing syndrome (SCS) represents a challenging endocrine disorder characterized by subtle autonomous cortisol secretion without the classic manifestations of overt Cushing syndrome. Early detection of SCS is critical due to its association with increased cardiovascular risk, metabolic syndrome, and potential progression to overt disease. This review synthesizes epidemiological data, explores pathophysiological mechanisms, discusses risk factors and diagnostic strategies, and highlights recent advances, guideline-based recommendations, and therapeutic approaches for clinicians engaged in the management of SCS.

Introduction

Subclinical Cushing syndrome occupies a unique niche in the spectrum of adrenal disorders, defined by mild, often asymptomatic, hypercortisolism. Unlike overt Cushing syndrome, SCS lacks classical stigmata such as central obesity, facial plethora, and muscle wasting. However, accumulating evidence underscores the syndrome’s significant morbidity, particularly in relation to metabolic and cardiovascular health. Early recognition and diagnosis are essential for optimizing outcomes, yet the subtlety of presentation poses considerable diagnostic dilemmas for clinicians.

Epidemiology / Disease Burden

The prevalence of SCS is estimated to range from 0.2% to 2% in the general population, rising to 5–20% among patients with incidentally discovered adrenal adenomas (adrenal incidentalomas). Epidemiological studies reveal that SCS disproportionately affects middle-aged and older adults, with a slight female predominance. Importantly, the disease burden is magnified by the elevated risk of hypertension, diabetes mellitus, dyslipidemia, osteoporosis, and vascular events, even in the absence of overt Cushingoid features. Longitudinal cohorts have demonstrated increased all-cause and cardiovascular mortality in affected individuals compared to matched controls.

Pathophysiology

SCS arises primarily from autonomous glucocorticoid secretion by adrenal adenomas. This hypercortisolism is often insufficient to suppress adrenocorticotropic hormone (ACTH) completely or produce florid clinical features. Molecular studies have identified aberrant expression of steroidogenic enzymes, somatic mutations (e.g., PRKACA), and disrupted feedback regulation within the hypothalamic-pituitary-adrenal (HPA) axis as key drivers. Chronic low-grade cortisol excess exerts insidious effects on glucose metabolism, vascular tone, bone remodeling, and immune function, culminating in gradual tissue injury and organ dysfunction.

Risk Factors

Risk stratification for SCS includes advanced age, female sex, presence of adrenal incidentaloma, obesity, poorly controlled hypertension, type 2 diabetes mellitus, and osteoporosis or fragility fractures without alternative explanation. The risk is also elevated in individuals with a history of unexplained cardiovascular events or metabolic syndrome. Genetic susceptibilities, such as familial clustering of adrenal tumors, are under investigation but remain incompletely defined.

Clinical Features

By definition, SCS lacks the overt clinical stigmata of Cushing syndrome. Nevertheless, subtle clinical clues may include resistant hypertension, impaired glucose tolerance or new-onset diabetes, central adiposity, proximal muscle weakness, and unexplained osteopenia or osteoporosis. Subtle neuropsychiatric symptoms, such as fatigue, mood disturbance, or cognitive impairment, may also be present and are often underappreciated in routine clinical practice. These non-specific features necessitate a high index of suspicion in at-risk populations.

Diagnosis

The diagnosis of SCS is predicated upon biochemical evidence of autonomous cortisol secretion, in the absence of overt clinical signs. Recommended initial screening tests include the overnight 1 mg dexamethasone suppression test (DST), late-night salivary cortisol, and 24-hour urinary free cortisol (UFC). Failure to suppress serum cortisol below 1.8 µg/dL (50 nmol/L) after DST, with normal or suppressed ACTH, supports the diagnosis. Additional testing may encompass plasma ACTH, dehydroepiandrosterone sulfate (DHEAS), and adrenal imaging to exclude malignancy. Interpretation of results must account for confounders such as stress, obesity, and concurrent medications. Given the lack of universally accepted diagnostic thresholds, a multidisciplinary approach involving endocrinology is advised.

Treatment & Management

Management decisions are individualized, balancing the potential benefits of intervention against surgical risks and patient comorbidities. Adrenalectomy is generally recommended for patients with biochemically confirmed SCS and comorbidities attributable to cortisol excess (e.g., hypertension, diabetes, osteoporosis). Conservative management with periodic monitoring may be appropriate for asymptomatic individuals or those with low biochemical activity. Medical therapy (e.g., steroidogenesis inhibitors) is reserved for patients unfit for surgery or with bilateral disease. Lifestyle modification and aggressive management of cardiovascular risk factors are universally indicated.

Recent Advances / Emerging Therapies

Recent advances in molecular diagnostics, including next-generation sequencing, have enhanced understanding of adrenal tumorigenesis and may facilitate risk stratification. Novel biomarkers, such as circulating steroid metabolites and microRNAs, are being explored for early detection and prognosis. Minimally invasive surgical techniques (e.g., laparoscopic adrenalectomy) have improved perioperative outcomes. The potential role of medical therapies, including selective glucocorticoid receptor modulators and inhibitors of steroidogenic pathways, is under active investigation in clinical trials.

Guideline Recommendations

Contemporary guidelines from the Endocrine Society and European Society of Endocrinology recommend screening for SCS in patients with adrenal incidentalomas, especially when metabolic or cardiovascular comorbidities are present. Biochemical confirmation using at least two independent tests is advised. Surgical intervention should be considered in those with proven cortisol autonomy and related comorbidities. Lifelong follow-up is essential to monitor for recurrence and manage long-term sequelae. Multidisciplinary collaboration is emphasized to optimize patient outcomes.

Conclusion

Subclinical Cushing syndrome is an underdiagnosed entity with significant clinical implications. Early detection relies on heightened clinical awareness, judicious use of biochemical testing, and careful risk assessment. Advances in molecular diagnostics and therapeutic strategies hold promise for more individualized management. Adherence to guideline-based recommendations and multidisciplinary care are paramount in reducing morbidity and improving prognosis among affected patients.