eMedicine Specialties > Radiology > Chest

Coccidioidomycosis, Thoracic

Author: Sat Sharma, MD, FRCP(C), FCCP, FACP, DABSM, Program Director, Associate Professor, Department of Internal Medicine, Divisions of Pulmonary and Critical Care Medicine, University of Manitoba; Site Director of Respiratory Medicine, St Boniface General Hospital
Coauthor(s): Bruce Maycher, MD, Director of Pulmonary Radiology, St Boniface General Hospital; Associate Professor, Department of Radiology, University of Manitoba
Contributor Information and Disclosures

Updated: Aug 9, 2007

Introduction

Background

Infection with Coccidioides immitis, a soil-inhabiting fungus, causes an illness in humans called coccidioidomycosis.

C immitis thrives in soil, and its growth occurs in either of 2 phases: the mycelial arthrospore phase in the soil and the spherule endospore phase in infected tissues. The mycelia are the least infectious, but the hyphae develop into arthrospores that become airborne and are highly infectious.

After the organism is inhaled into the lungs, the arthrospore develops into a thick-walled spherule that is filled with endospores. Once it is released, each endospore can start the development of a new spherule, and the infection in the host progresses. Coccidioidomycosis is not known to transmit from person to person.

The risk of infection is the highest in the dry summer months; a secondary period of high risk usually occurs in the late fall, terminating with winter rains. Dust exposure is a critical route for C immitis infection; individuals who dig in the soil or who are exposed to the disrupted earth are at the greatest risk.

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Pathophysiology

Depending on the immune response of the host, a C immitis infection may evolve into 1 of many clinical syndromes. Most patients with primary pulmonary coccidioidomycosis are asymptomatic, and the infection resolves spontaneously. In approximately 5% of patients, a persistent pulmonary focus of coccidioidomycosis may be manifested as a nodule, a cavity, or a chronic, progressive pneumonia. In approximately 5-7% of cases, coccidioidal pneumonia evolves to form a sharply circumscribed and (usually) noncalcified pulmonary nodule.

Cavity formation occurs in approximately 5% of patients; these cavities are commonly asymptomatic, and approximately 50% of them disappear within 2 years of occurrence. Some patients develop chronic, progressive coccidioidal pneumonia, which manifests as chronic systemic symptoms, such as low-grade fever, weight loss, cough, chest pain, and hemoptysis.

In addition, C immitis can disseminate from the lungs and thoracic cavity to infect other organs, such as bone, joints, skin, and meninges. Dissemination usually occurs within weeks or months of the primary pneumonia. However, in some patients with disseminated disease, radiographs may not show evidence of previous pulmonary disease, and the patients will have no history of a preceding respiratory illness. Dissemination is more likely to occur in individuals belonging to certain ethnic groups, including African Americans and Filipinos. This is also true for patients with depressed cellular immunity, including those with lymphoma or human immunodeficiency virus (HIV) infection, individuals who have undergone organ transplantation, and patients receiving high-dose corticosteroids.

Frequency

United States

Coccidioidomycosis affects an estimated 100,000 people annually in the United States. Endemic areas in the United States include Arizona, south central California, Nevada, and New Mexico, as well as the western half of Texas. Although usually affecting people in endemic areas, coccidioidomycosis is increasingly recognized outside these regions, as travelers passing through them are exposed to C immitis.

International

The fungus is endemic to certain regions of North America and South America. Affected areas are in the lower Sonoran areas, which are characterized by semiarid regions with hot summers and alkaline soils. These areas include northern Mexico, as well as Central America and South America. Central American countries in which this fungus is ubiquitous include regions of Mexico bordering the western United States, Guatemala, Honduras, and Nicaragua. The disease is also endemic in such areas as the desert regions of South America, which encompasses Argentina, Paraguay, and Venezuela.

Mortality/Morbidity

Infection is directly related to the degree of exposure to airborne arthrospores. Persons exposed to large amounts of dust in endemic areas (eg, farmers, archaeologists) have higher rates of infections. Infection rates usually are calculated from coccal skin-test results.

Approximately 40% of infected patients have symptomatic disease, usually pulmonary. In about 90% of cases, the pulmonary infection resolves without sequelae; however, 5-10% of patients develop chronic disease with pneumonia, cavitary lesions, and nodules. In less than 1% of cases, the disease progresses to dissemination.

Race

The primary pulmonary disease shows no racial predilection. However, certain races appear to have a greater susceptibility to the disseminated disease, including, in descending order, Filipinos, African Americans, Hispanics, Native Americans, and Asians. Blacks have a 5 times greater risk of developing coccidioidomycosis-related meningitis than do whites, and they have a 5 times greater risk of dying from coccidioidomycosis than do whites. The risk of developing meningitis is 10 times greater for Filipinos than it is for whites.

Sex

Pregnant women are predisposed to progressive and disseminated infections, particularly in the third trimester. This likely occurs because pregnancy is associated with a weakening of cell-mediated immunity. A pregnant woman's risk of developing disseminated coccidioidomycosis is 40-100 times greater than that of the general population.

Presentation

After C immitis is inhaled, an initial pyogenic infection develops. This is followed by a granulomatous respiratory infection. In most patients, the asymptomatic pulmonary infection resolves spontaneously. However, in approximately 5% of patients, a persistent pulmonary focus or dissemination to other parts of the body (eg, bone, joints, skin, meninges) occurs. The infection may also spread to the bone marrow, myocardium, and kidneys.

Risk factors

Disseminated coccidioidomycosis may occur in an otherwise healthy individual, but several risk factors have been identified:

• Male sex
• Ethnicity (eg, African American, Filipino race)
• Pregnancy
• Diabetes
• Depressed cellular immunity, as in patients with lymphoma or HIV infection, patients who have undergone organ transplantation, or patients who are receiving high-dose corticosteroids

Medical history

Approximately 30-40% of individuals have clinical symptoms after infection. The incubation period, after infection and before symptoms appear, is usually 7-21 days. The disease spectrum ranges from a mild, flulike illness to subacute pneumonia. Most patients have a cough, chest pain, fever, and fatigue.

Physical examination

More than 50% of cases in people residing in high-risk, endemic areas are subclinical. Coccidioidomycosis should be considered in individuals who are at risk of infection and in those who have a constellation of nonspecific signs or unusual rashes, such as erythema nodosum, erythema multiforme, toxic erythema, and arthralgias.

Signs of synovitis, bony tenderness, osteomyelitis, meningitis, hydrocephalus, lymphadenopathy, and abdominal masses or tenderness may indicate a coccidioidal infection. Other systemic organ involvements include the following:

• Skin
  • A wide variety of rashes, including maculopapular lesions, erythema multiforme, and erythema nodosum, may develop.
  • The development of erythema nodosum is an indicator of a good prognosis.
• Pulmonary
  • Bronchitis, bronchiolitis, reactive airways disease, pneumonia, and pleural effusions may develop.
  • Frank empyemas and bronchopleural fistulas are possible.
• Musculoskeletal
  • One third of patients with dissemination have musculoskeletal involvement.
  • Bone lesions are unifocal in 60% of cases, and joint lesions are unifocal in 90% of cases.
  • Multiple lesions or vertebral lesions are associated with a poor prognosis.
• Central nervous system
  • Acute or chronic meningitis is possible.
  • Acute hydrocephalus may be the first sign of disseminated coccidioidomycosis.

Laboratory studies

The 2 tests that are used to diagnose pulmonary coccidioidomycosis are sputum cultures and serum coccidioidal antibody tests.

• Sputum culture
  • The isolation of C immitis from a sputum specimen establishes the diagnosis.
  • The identification of spherules in the direct examination of sputum also is diagnostic, but this is less sensitive than a culture finding.
  • The organism usually grows within 5 days on most routine microbiologic media.
  • A negative culture finding does not rule out coccidioidomycosis.
• Coccidioidal antibody tests
  • Two serologic tests are available to detect immunoglobulin G (IgG) antibodies: the precipitin test (TP) and the complement fixation (CF) test.
  • A negative antibody test result does not rule out the disease.

Preferred Examination

Chest radiography is readily available and is usually the first imaging study performed. It assists in clinical staging of the disease and is useful in following up the progression or resolution of the disease. However, chest radiographic findings are nonspecific and variable.

Asymptomatic patients may have normal chest radiographic findings, and a normal result generally excludes significant clinical disease. The chest radiographic findings may progress from single or multiple areas of airspace consolidation to the formation of nodules or cavities, which may further progress to diffuse reticulonodular lung disease and upper-lobe scarring.

In a patient who is either living in or has visited an endemic area, the chest radiographic findings described in the following sections are highly suggestive of thoracic coccidioidomycosis. The diagnosis must be established by means of cultures, histopathologic examination, or serologic tests.

Limitations of Techniques

Chest radiographic findings alone are not diagnostic of thoracic coccidioidomycosis, because other infectious diseases and neoplastic processes may mimic the disorder.

Differential Diagnoses

Other Problems to Be Considered

Other fungal infections
Lymphoma
Other causes of cough, fever, and fatigue
Old granuloma

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