Coccidioidomycosis (Valley Fever) Imaging

Introduction:

Coccidioidomycosis or Valley fever is a disease caused by the soil-inhabiting fungus Coccidioides. It is also known as San Joaquin Valley fever, as it is endemic to the arid areas of the Western Hemisphere. It was first discovered in the year 1892 and named Coccidioides immitis. Coccidioides commonly grow in soil containing high salt content and agar as filaments or mycelia. Coccidioides is endemic to New Mexico, Nevada, California, Utah, and Arizona. The diagnosis of this condition is based on various tests, and the time it takes to get the test results mainly depends on the type of test. Blood tests take a few days to get the rest, and other cultured tests in the laboratory take a few days to weeks to give out the results.

What Are the Causes of Coccidioidomycosis?

Coccidioidomycosis is caused by a dimorphic fungus called Coccidioides that exists as spherules or mycelia. Both of them are asexual forms. The coccidioides genus contains two species: Coccidioides immitis and Coccidioides posadasii. C.immitis is commonly found in California, and C.posadasii is expected in the United States and other parts of the world. The susceptibilities and clinical manifestations of the two species are the same and can be differentiated only by molecular methods.

What Is the Pathophysiology of Coccidioidomycosis?

Mycelia grow by forming septae, and within a week, the mycelial cells undergo cell wall thinning and autolysis. Some of them transform into barrel-shaped arthroconidia, which are loosely connected and become airborne. Arthroconidia are smaller infectious particles that measure about two to five microns and reach the terminal bronchiole when inhaled. When the arthroconidia reach the lungs, they remodel from rectangular to spherical-shaped spherules. The spherules can grow up to the size of 75 microns and are divided by internal septae into compartments. Each compartment contains endospores. The spherules may rupture and release endospores in the alveolar sacs that cause acute inflammation and host response. Coccidioides grow well on bacteria or mycologic media after a week of incubation, and the colonies appear white.

What Are the Signs and Symptoms of Coccidioidomycosis?

About 60 percent of coccidioidomycosis is asymptomatic, and sometimes they show symptoms that appear seven to 21 days after exposure to the fungus. The symptoms are:

• Fever.

• Cough.

• Chest pain.

• Sore throat.

• Shortness of breath.

• Headache.

• Weight loss.

• Hemoptysis (coughing up blood mixed with sputum).

• Rashes (maculopapular).

• Migratory arthralgia (swelling in one or more joints in which pain migrates from one joint to another).

• Erythema nodosum (painful nodules formed by the inflammation of the fat cells).

• Erythema multiforme (a skin disease characterized by painful, raised rashes).

• Night sweats.

• Nausea (urge to vomit).

• Vomiting.

• Visual changes.

What Are the Imaging Techniques Used in the Diagnosis of Coccidioidomycosis?

Chest Radiography:

• In coccidioidomycosis, chest radiography shows localized infiltrates. Pleural effusion, hilar adenopathy (enlargement of hilar lymph nodes), and diffuse reticulonodular disease are also seen.

• Miliary disease, thin-walled single or multiple cavities, and pneumothorax (air collection outside the lungs but within the pleural or lung cavity) are also less commonly seen.

• Even though coccidioidomycosis is detected in chest radiography, it requires additional imaging techniques for confirmation.

• Sometimes calcification is seen in coccidioidomycosis, but it is rare compared to histoplasmosis and tuberculosis (bacterial infection of the lungs).

Computed Tomography (CT) Scan:

• A CT scan shows endobronchial coccidioidal granulomas, pulmonary nodules (clumps of cells in the chest), pneumatoceles (single or multiple air-filled cysts in the thin-walled structures), and bronchiectasis (thickening and widening of the bronchi due to infection and inflammation).

• Mycetoma (skin infection caused by bacteria or fungus), pleural effusion (abnormal collection of fluid between the lining of the lung and chest), hydropneumothorax (abnormal collection of fluid and air in the pleural cavity), mediastinal and paratracheal adenopathy, and empyema (collection of pus in the space between chest and lungs) are also seen.

• A CT scan shows abscesses, granulomas, and basilar meningeal enhancement in brain involvement cases.

• Bony destruction in coccidioidomycosis is more enhanced in CT scans than in Magnetic Resonance Imaging (MRI).

• Ground glass attenuation in CT scan indicates granulomatous inflammation.

• In acute pulmonary coccidioidomycosis, nodular areas appear as areas of homogenous attenuation that are separated by the thickened interlobular septum associated with lymph node enlargement and pleural effusion.

• CT-guided transthoracic core needle biopsy (CTTCB) is a safe method for evaluating pulmonary nodules in coccidioidomycosis.

• It shows about 83 percent sensitivity and 100 percent specificity in diagnosing coccidioidomycosis.

Magnetic Resonance Imaging (MRI):

• In MRI, the findings of coccidioidomycosis include soft tissue involvement and heterogeneous marrow signal intensity.

• MRI helps detect the extent of the lesion in joints, bone, and soft tissues, including fistulae and sinus tracts.

• CNS (central nervous system) involvement in coccidioidomycosis shows hydrocephalus, vascular occlusion, ventricular enlargement, and basilar meningitis.

• MRI is an excellent tool for detecting cases suspected of spinal cord impingement, planning the surgical debridement of affected areas, and determining the extent of the lesion.

• Coccidioidomycosis involvement manifests in the spinal cord as osteomyelitis discitis (infections in the spine), an expanded leptomeningeal region, arachnoiditis (inflammation of the arachnoid mater), and cord edema.

Positron Emission Tomography (PET) Scan:

• The PET scan is now increasingly used for staging and diagnosing fungal infections, including coccidioidomycosis.

• Fluorodeoxyglucose PET (FDG-PET) is a radioactive tracer that images active coccidioidomycosis.

• Disseminated coccidioidomycosis shows diffuse uptake, whereas solitary nodules are similar to malignancy, and longstanding granulomas show less or no uptake.

• Pulmonary nodules of coccidioidomycosis take up less FDG by positron emission computed tomography (PET or CT) scans than malignancy.

What Is the Management and Treatment of Coccidioidomycosis?

Based on the severity of the condition, the healthcare provider decides the management plan for coccidioidomycosis. The doctor usually monitors the patient’s symptoms before prescribing the medication, or they might treat it with antifungal medications to reduce the risk of serious illness. The commonly used medications for the treatment of coccidioidomycosis include

• Itraconazole.

• Fluconazole.

• Amphotericin B.

What Are the Differential Diagnoses of Coccidioidomycosis?

• Granuloma - A granuloma is an area of inflammation or closely packed immune cells in the body.

• Blastomycosis - A fungal infection caused by Blastomyces dermatitidis.

• Lung Abscess - Fluid-filled sac found in lung tissues.

• Lung cancer.

• Histoplasmosis - Fungal infection caused by inhalation of spores found in bat and bird droppings.

• Eosinophilic pneumonia - A group of diseases characterized by eosinophilic infiltrates in the lung parenchyma.

• Enteropathic Arthropathies - A type of arthritis (joint pain) that causes tenderness and inflammation in the legs, arms, or spine.

• Lymphoma - Tumor of the lymphatic system.

• Myelophthisic anemia - A type of anemia in which immature erythrocytes are found in the blood.

Conclusion:

Chest radiography shows higher sensitivity for coccidioidomycosis in patients from endemic areas but shows less specificity. In addition, primary nodules in coccidioidomycosis are more enhanced in CT lungs when intravenous contrast agents are administered than in chest radiographs. The treatment options for coccidioidomycosis include medications such as Diflucan or Itraconazole. Coccidioidomycosis is more common in older adults aged between 69 to 79 years old. Weight loss of more than ten percent, prominent hilar adenopathy, and Complement Fixation (CF) antibody titer greater than 1:16 should be considered and treated with oral Azole.