Illustration of blastomycosis infection in the lungs, resembling a hidden fungal network.

Blastomycosis: When a TB Diagnosis Misses a Deadly Fungal Infection

Lena Voss in Health & Wellness July 2025 • 4 min read.

"A Chicago man's journey from misdiagnosis to recovery highlights the challenges and importance of accurate fungal infection detection."

Imagine battling a persistent cough, fever, and unexplained weight loss, only to be told you have tuberculosis (TB). You begin treatment, but your condition doesn't improve. This was the reality for a 36-year-old man from Chicago, whose initial diagnosis of TB masked a far more insidious threat: disseminated blastomycosis.

Blastomycosis is a fungal infection caused by Blastomyces species. While endemic to regions like the Mississippi, Ohio, and St. Lawrence River valleys, and the Great Lakes area, it can occur worldwide. The fungus typically enters the body through the lungs, but it can spread to other organs, including the bones, skin, and central nervous system. This ability to mimic other diseases makes blastomycosis a diagnostic challenge.

The case of the Chicago man underscores the critical importance of considering blastomycosis in patients presenting with respiratory symptoms, especially in endemic regions. His journey from misdiagnosis to eventual recovery offers valuable insights into the challenges and potential pitfalls of diagnosing this elusive fungal infection.

The Case: A Diagnostic Odyssey

Illustration of blastomycosis infection in the lungs, resembling a hidden fungal network.

The 36-year-old Hispanic patient initially presented with right arm weakness and tingling, along with a persistent cough, blood-streaked sputum, fever, and recent weight loss. Two months prior, he had been diagnosed with pulmonary TB at an outside hospital after experiencing hemoptysis and night sweats. Despite denying any TB exposure, travel, or contact with sick individuals, he was started on standard TB treatment.

However, his condition did not improve. Upon admission to another hospital, a chest X-ray revealed a dense consolidation in his right upper lung. A computed tomography (CT) scan confirmed a 9.2 cm mass in the same area. Further complicating the picture, a magnetic resonance imaging (MRI) of the brain showed small enhancing lesions in the right frontal cortex, left cerebellar hemisphere, and upper cervical cord. Despite these findings, initial sputum cultures were negative for bacteria, fungi, and mycobacteria.

Initial Misdiagnosis: The patient's symptoms initially led to a diagnosis of pulmonary tuberculosis (TB).
Persistent Symptoms: Despite TB treatment, symptoms like cough, fever, and weight loss persisted.
Brain Lesions: MRI revealed lesions in the brain, complicating the diagnostic picture.
Negative Sputum Cultures: Initial tests failed to identify any bacteria, fungi, or mycobacteria.

Ultimately, a broncho-alveolar lavage (BAL) confirmed the presence of Blastomyces spp., leading to the correct diagnosis. The patient's TB treatment was discontinued, and he was started on intravenous liposomal Amphotericin B, followed by oral Itraconazole. After two months, he was asymptomatic, and follow-up imaging showed significant resolution of the lesions. He remained symptom-free after nearly a year.

The Takeaway: Think Fungal!

This case underscores the importance of considering blastomycosis in the differential diagnosis of patients presenting with respiratory and neurological symptoms, especially in endemic areas. Early diagnosis and appropriate treatment can prevent disease progression and improve patient outcomes. When symptoms persist despite initial treatment, it's crucial to consider less common infections like blastomycosis and pursue further diagnostic testing.

About this Article -

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Everything You Need To Know

What is Blastomycosis, and how does it differ from Tuberculosis (TB)?

Blastomycosis is a fungal infection caused by the Blastomyces species. It primarily affects the lungs, but can spread to other parts of the body. Unlike Tuberculosis (TB), which is a bacterial infection, Blastomycosis is caused by a fungus. Both can present with similar respiratory symptoms like cough and fever, which can lead to misdiagnosis. A key difference lies in the causative agent and the treatment required; TB is treated with antibiotics, while Blastomycosis requires antifungal medications such as Amphotericin B and Itraconazole.

What are the key symptoms and risk factors associated with Blastomycosis?

Common symptoms of Blastomycosis include persistent cough, fever, unexplained weight loss, and potentially neurological symptoms like weakness and tingling. Risk factors primarily involve living in or visiting endemic regions, particularly the Mississippi, Ohio, and St. Lawrence River valleys, as well as the Great Lakes area. Exposure to soil containing the Blastomyces fungus increases the risk. The infection often starts in the lungs but can disseminate to other organs, including the bones, skin, and brain, making early diagnosis crucial.

Why is Blastomycosis often misdiagnosed, and what are the consequences of such misdiagnosis?

Blastomycosis is often misdiagnosed because its symptoms, such as cough and fever, can mimic those of other respiratory illnesses, including Tuberculosis (TB). This similarity in symptoms makes it challenging to differentiate between the two without specific diagnostic tests. A misdiagnosis of Blastomycosis as TB can lead to inappropriate treatment, as the standard TB treatment is ineffective against the fungal infection. The consequences include a lack of improvement in the patient's condition, potential disease progression, and the spread of the infection to other organs, leading to severe complications.

What diagnostic steps are crucial in identifying Blastomycosis, especially when TB treatment fails?

When initial treatment for TB fails, further diagnostic testing is essential. This may include a chest X-ray or CT scan to assess lung involvement, and an MRI to evaluate potential spread to the brain or other organs. The presence of lesions in the lungs or brain should raise suspicion. Specific diagnostic tests, such as broncho-alveolar lavage (BAL) to identify Blastomyces spp., and other fungal cultures and tests are critical for confirmation. The case highlights that when symptoms persist despite initial treatment, considering less common infections like Blastomycosis and pursuing further diagnostic testing is critical.

How is Blastomycosis treated, and what is the prognosis for patients?

The primary treatment for Blastomycosis involves antifungal medications. Intravenous liposomal Amphotericin B is often used initially for severe cases, followed by oral Itraconazole. The prognosis for patients with Blastomycosis is generally good, especially with early diagnosis and appropriate treatment. In the case presented, the patient's symptoms resolved after two months of antifungal treatment, and follow-up imaging showed significant improvement. However, the outcome depends on the severity of the infection, the extent of spread, and how quickly the correct diagnosis and treatment are implemented. Continued monitoring and follow-up are crucial to ensure complete recovery and prevent recurrence.