Opinions/Hypotheses

“Imitators” of the ARDS: Implications for Diagnosis and Treatment

Prevalence of Diffuse, Noninfectious Parenchymal Lung Disease Mimicking ALI/ARDS

In the absence of a prospective study of consecutive patients meeting the diagnostic criteria for ALI/ARDS who undergo lung biopsy, it is not possible to know how frequently the acute diffuse, noninfectious parenchymal diseases meet the diagnostic criteria for ALI/ARDS. It is clear, however, that that many patients with these conditions fit the definition of ALI/ARDS. The most common predisposing causes of ALI/ARDS in most series are trauma, aspiration, and sepsis.³⁴⁵⁶⁷ However, approximately

The “Imitators”

Table 1 lists the histologic patterns, usual etiologies, and BAL cellular constituents of the acute noninfectious parenchymal lung diseases that often meet ALI/ARDS criteria. These noninfectious pneumonias have protean manifestations, many of which suggest an infectious process. These include fever, myalgias, nonproductive cough, and progressive dyspnea.⁹¹⁰ The WBC counts, erythrocyte sedimentation rates, and C-reactive protein and serum lactic dehydrogenase levels are often elevated.

Evaluation of the Imitators

In patients who present with an acute, noninfectious, parenchymal lung disease without a recognized ALI/ARDS risk factor, the possibility of an illicit or prescribed drug, a systemic immunologic disease, or an environmental exposure being the cause must be considered along with infection. Various classes of drugs, particularly chemotherapeutic agents, can manifest as any of the histologic categories in Table 1.^{53545556575859} An acute immunologic pneumonia complicating a CVD can present with

Role of BAL

BAL should be performed early on and preferably after tracheal intubation. The samples should be sent for identification of selected infectious agents and a differential WBC count (Table 1). In addition to excluding the possibility of the occasional diffuse fulminant viral or atypical pneumonia due to Mycoplasma pneumoniae, Legionella pneumophiliaor Chlamydia pneumoniae in the immunocompetent host, the results of the differential WBC count may obviate the need for further intervention. BAL

Treatment of the Imitators

Data regarding the effectiveness of treatment of the acute, noninfectious parenchymal lung diseases come from individual reports and small case series. The literature also suffers from considerable variability in the timing, dosing, and duration of treatment. In general, corticosteroids are recommended. In addition, depending on the specific disorder, immunosuppressive drugs are added. Plasmapheresis is recommended for patients with ABMA disease.⁶³

There are > 90 cases of AIP recorded in the

Summary

When confronted with a case of acute respiratory failure severe enough to meet the diagnostic criteria of ALI/ARDS but without a predisposing cause, it is important to consider the alternate diagnoses reviewed above, and to attempt to establish a diagnosis as expediently as possible utilizing BAL with differential counts and, if necessary, the consideration for surgical biopsy. The most common error is that the episode of respiratory failure is incorrectly attributed to an infectious pneumonia