A Silent Invader: Asymptomatic Rhodococcus Infection Unmasked in A Patient with Ectopic ACTH-Dependent Cushing's Syndrome.

Introduction: Rhodococcus species, particularly Rhodococcus equi, are rare opportunistic pathogens that typically affect immunocompromised individuals. These infections usually present with respiratory or systemic symptoms and are often linked to environmental exposure. Asymptomatic Rhodococcus infections are exceedingly rare and pose unique diagnostic and therapeutic challenges.

Case description: We report the case of a 29-year-old male who presented with new-onset diabetes mellitus, resistant hypertension and significant weight gain. Physical examination revealed features consistent with Cushing's syndrome. Biochemical evaluation confirmed ACTH-dependent hypercortisolism with an elevated plasma ACTH level, and a lack of suppression on high-dose dexamethasone testing; imaging identified a suspicious pulmonary nodule. Bronchoscopic biopsy revealed no malignancy, however cultures grew Rhodococcus species. The patient denied any respiratory symptoms or environmental exposure. Initial antibiotic therapy with ciprofloxacin and rifampin was started. Follow-up imaging showed rapid enlargement of the pulmonary mass, prompting surgical resection. Histopathology revealed malakoplakia, and repeat cultures again yielded Rhodococcus spp. Antibiotics were adjusted to azithromycin and rifampin, and the patient was started on ketoconazole to manage hypercortisolism.

Conclusion: This case highlights the importance of considering opportunistic infections such as Rhodococcus spp. in immunocompromised patients, even in the absence of symptoms. It underscores the diagnostic value of investigating incidental findings in such populations and illustrates the need for prompt, multidisciplinary management to prevent disease progression.

Learning points: This case highlights the diagnostic complexity of incidental pulmonary nodules in immunocompromised patients, reinforcing the need for thorough microbiological investigation even in the absence of infection symptoms.It illustrates a rare, asymptomatic presentation of Rhodococcus infection in the context of ectopic ACTH-dependent Cushing's syndrome, a scenario not widely reported in the literature.Practical is given guidance on managing opportunistic infections and evaluating ectopic ACTH sources, aiding internists in navigating similar diagnostic and therapeutic challenges in complex endocrine-infectious overlaps.