Blastomycosis Masquerading as Tuberculosis: A Diagnostic Challenge in a Patient With Diabetes

Blastomycosis is an endemic fungal infection caused by Blastomyces dermatitidis. Immunosuppressed individuals, as well as those with diabetes mellitus or obesity, are more likely to develop severe disease. It is often referred to as "the great imitator" because it can closely mimic tuberculosis. Early diagnosis is critical to prevent delays in appropriate treatment and avoid complications. We present the case of a 51-year-old Haitian immigrant with poorly controlled diabetes mellitus who was initially diagnosed and treated for tuberculosis based on a positive interferon-gamma release assay (IGRA). Despite receiving RIPE (rifampin, isoniazid, pyrazinamide, and ethambutol) therapy, his symptoms failed to improve. Further comprehensive evaluation ultimately revealed disseminated blastomycosis with pulmonary and cutaneous involvement. He was successfully treated with liposomal amphotericin B, followed by itraconazole. This case underscores the diagnostic challenges of blastomycosis, particularly in immunocompromised individuals. In endemic areas, a high index of clinical suspicion and appropriate diagnostic testing are crucial to avoid misdiagnosis and to ensure timely and effective treatment.