Coccidioidomycosis refers to an infection caused by the dimorphic fungus Coccidioides spp, usually localised to the lungs. This disease is not to be confused with the similarly named paracoccidioidomycosis.

The most common forms of Coccidioides spp are Coccidioides immitis and Coccidioides posadasii 1. These species are endemic to many desert regions of North, Central and South America, especially in the American state of Arizona 1. The disease can occur in hosts with a well-functioning immune system, especially with repeated exposure, but the risk is increased if one is immunocompromised.

The disease is often subclinical and asymptomatic in approximately 50% of patients, especially among hosts with an intact immune system and/or those with minimal exposure 2. Those who do develop symptoms, often manifest with a pulmonary disease in the form of coccidioidal pneumonia, also known colloquially as valley fever 2. This is characterised by cough, chest pain, fever, headache, and fatigue 2. In many patients, there are often associated constitutional symptoms and cutaneous manifestations such as erythema nodosum 2,4.

Disseminated coccidioidomycosis usually manifests in patients who are immunocompromised 3. In a study of patients with concurrent HIV, the most common features were diffuse bilateral pulmonary pneumonia (similar to PCP pneumonia), widespread lymphadenopathy, skin involvement, and CNS coccidioidomycosis which mainly presents as severe meningitis 3. Bone and joint involvement also often occurs in disseminated coccidioidomycosis, although are notably less common in patient with HIV compared to those immunocompromised from other means 3. It should be noted that disseminated or extra-pulmonary coccidioidomycosis is an AIDS defining illness.

Infection generally occurs after inhalation of a single arthroconidium 1. Once within the lung, the arthroconidia become spherules that grow as they mature before rupturing and releasing endospores 1. These endospores are then able to disseminate throughout the lung locally, but also spread haematogenously via the blood stream 1. Each endospore is capable of transforming into another spherule and repeating the infective process 1.

The disease can have a variety of radiographic presentations depending on the area of the body involved and the modality of imaging used 4,5.

Parenchymal consolidation is the most common (75%) imaging feature, associated nodules, hilar lymphadenopathy and pleural effusions may be appreciated 4,5. These changes may also be transient and seem to improve in some parts of the lung while advancing in others 4,5. See pulmonary coccidioidomycosis for a more comprehensive description.

Any bone can be affected, although those of the axial skeleton (especially vertebrae) are most common 4. Lesions are often multiple, and tend to be lytic in appearance 4. Osteomyelitis may or may not be additionally present 4. Skull lesions are also common, which is unusual in comparison to other granulomatous infectious diseases 4. Joint involvement usually manifests as a monoarticular arthritis, typically in either the ankles or knees, and is usually an extension of nearby osteomyelitis 4. Affected joints demonstrate imaging features consistent with synovitis, joint effusion, bony destruction and erosions 4. Although various radionuclide scans may be useful for detecting bone and joint involvement, MRI is the most sensitive modality 4.

The primary CNS manifestation is coccidioidal meningitis, which has a variety of features including hydrocephalus, cerebral infarction, vasculitis and associated subarachnoid haemorrhage, and abscesses 4,6. MRI is the most sensitive sequence for detecting leptomeningeal enhancement (on post-contrast gadolinium images) that is classic of this disease process 4,6. See CNS coccidioidomycosis for a more comprehensive description.

The mainstay of medical treatment is with fluconazole 7. Surgical opinion may also be sought for CNS involvement or complications of pulmonary coccidioidomycosis if necessary 7

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Cases and figures

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    Figure 1: mechanism
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    Case 1: pulmonary disease
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    Case 2: bone and joint disease
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