Fever after recent travel

DIFFERENTIAL DIAGNOSIS

1. Which of the following is not in the differential diagnosis?

• Disseminated tuberculosis
• Coccidioidomycosis
• Subacute infective endocarditis
• Disseminated histoplasmosis
• Blastomycosis

Although the patient has a systemic disease, subacute infective endocarditis is not likely because of a lack of predisposing factors such as a history of endocarditis, abnormal or artificial heart valve, or intravenous drug abuse. Moreover, negative blood cultures and the absence of vegetations on echocardiography make endocarditis very unlikely.

Given that the patient is immunosuppressed, opportunistic infection must be at the top of the differential diagnosis. Histoplasmosis, coccidioidomycosis, and blastomycosis are endemic in Mexico. Disseminated histoplasmosis is the most likely diagnosis; coccidioidomycosis and blastomycosis are less likely, based on the history, signs, and symptoms. Disseminated tuberculosis must be excluded before other diagnostic possibilities are considered.

TUBERCULOSIS IN PATIENTS ON TNF-ALPHA ANTAGONISTS

Tuberculosis has been reported in patients taking TNF-alpha antagonists.¹ The frequency of tuberculosis is much higher than that of other opportunistic infections, and over 50% of reported cases involve extrapulmonary tissues in patients treated with TNF-alpha antagonists.²

British Thoracic Society guidelines recommend screening for latent tuberculosis before starting treatment with a TNF-alpha antagonist; the screening should include a history of tuberculosis treatment, a clinical examination, chest radiography, and a tuberculin skin test.³ Patients found to have active tuberculosis should receive a minimum of 2 months of standard treatment before starting a TNF-alpha antagonist. Patients with evidence of past tuberculosis or a history of tuberculosis who received adequate treatment should be monitored regularly. Patients with prior tuberculosis not adequately treated should receive chemoprophylaxis before starting a TNF-alpha antagonist.

Fever, night sweats, and intrathoracic and intra-abdominal lymphadenopathy are common features of disseminated tuberculosis. Upper-lobe cavitary disease or miliary lesions may be seen on chest radiography, but atypical presentations with lower-lobe infiltrate are not uncommon in immunosuppressed patients.⁴

A negative tuberculin skin test and a normal chest radiograph 3 months ago, along with negative sputum and bronchial lavage fluid cultures and no history of tuberculosis contact, make tuberculosis unlikely in our patient.

COCCIDIOIDOMYCOSIS

Coccidioidomycosis (valley fever) is caused by the fungus Coccidioides immitis, which lives in the soil and is acquired by inhalation of airborne microscopic spores.

Fatigue, cough, fever, shortness of breath, headache, night sweats, muscle or joint pain, and a rash on the upper body or legs are common symptoms. It may cause a self-limiting flulike illness. From 5% to 10% of patients may develop serious long-term lung problems. In a small number of patients, the disease may progress beyond the lungs to involve the central nervous system, spinal cord, skin, bones, and joints.⁵

Serologic testing is highly useful for the diagnosis. Antigen testing has a sensitivity of 71% and a specificity of 98% for the diagnosis, but cross-reactivity occurs in 10% of patients with other types of mycosis. Respiratory secretions and tissue samples should undergo microscopic study and culture.

BLASTOMYCOSIS

Blastomycosis is caused by the fungus Blastomyces dermatitidis, which lives in soil and in association with decomposing organic matter such as wood and leaves. Inhalation of spores may cause a flulike illness or pneumonia. In serious cases, the disease can spread to skin and bone.

The diagnosis is established with fungal cultures of tissue samples or body fluids (bone marrow, liver tissue, skin, sputum, blood). Rapid diagnosis may be obtained by examination of the secretions under a microscope, where typical broad-based budding yeast can be seen in almost 90% of cases.⁶ Antigen may also be detected in urine and serum⁷; the sensitivity of antigen testing is 93% and the specificity is 98%. Serologic testing is not recommended for diagnosis of blastomycosis because of poor sensitivity and specificity.⁸

NARROWING THE DIFFERENTIAL

Both coccidioidomycosis and blastomycosis should be included in the differential diagnosis of a systemic disease with subacute onset and prominent lung involvement in a patient returning from travel to Mexico. The lack of involvement of the central nervous system, spinal cord, bones, or joints makes these infections less likely in our patient.

However, swimming in a cenote under a rock formation is an important clue to the diagnosis in our patient, as it puts him at risk of inhaling microconidia or hyphal elements of histoplasmosis. This, along with his immunocompromised status, fever, hemoptysis, night sweats, skin and lung features, and the generally subacute course of his illness, make disseminated histoplasmosis the most likely diagnosis.

Radiologic findings of pulmonary infiltrate with effusion and elevated lactate dehydrogenase, aminotransferases, and alkaline phosphatase increase the likelihood of disseminated histoplasmosis.