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How do I determine the cause?

Constructing and Ranking a DDx


Figure 10-1.

Initial approach to patients with cough and congestion.

The differential diagnosis of acute cough and congestion ranges from trivial self-limited upper respiratory viral infections to serious, imminently life-threatening pneumonia. Importantly, there are many causes of pneumonia that need to be identified in order to make an accurate diagnosis and provide appropriate treatment.

Differential Diagnosis of Acute Cough and Congestion

  1. Common cold

  2. Sinusitis

  3. Bronchitis

  4. Influenza

  5. Pertussis

  6. Pneumonia

    1. Community-acquired pneumonia (CAP)

    2. Hospital-acquired pneumonia

    3. Aspiration pneumonia

    4. Tuberculosis (TB)

    5. Opportunistic (eg, Pneumocystis jirovecii pneumonia [PJP])

The approach to such patients focuses on 2 pivotal questions. First, does the patient have symptoms, signs, or risk factors for pneumonia that warrant a chest radiograph or other evaluation? Second, in patients with pneumonia, is it a CAP vs. another type of pneumonia (such as PJP, aspiration pneumonia, TB, etc.) that requires additional diagnostic evaluation and/or treatment?

  1. The diagnosis of pneumonia is usually based on clinical findings (cough, fever, crackles), accompanied by infiltrate on chest film. Microbiologic confirmation is usually unnecessary.

  2. When evaluating a patient who has acute respiratory symptoms it is imperative to determine who is likely to have pneumonia and therefore needs a radiograph to evaluate their symptoms.

  3. Prevalence of symptoms in patients with pneumonia

    1. Cough, 96%

    2. Fever, 81% but 53% in the elderly

      image Elderly patients with pneumonia often do not have a fever. Clinicians should have a low threshold for obtaining a chest radiograph in elderly patients with a cough.

    3. Dyspnea, 46–66%

    4. Pleuritic chest pain, 37–50%

    5. Chills, 59%

    6. Headache, 58%

  4. Physical exam

    1. No single finding is very sensitive. Therefore, the absence of any single finding does not rule out pneumonia (Table 10-1).

      1. Neither a normal lung exam nor the absence of fever rule out pneumonia (LR–, 0.6 and 0.8, respectively).

        image A normal lung exam does not rule out pneumonia.

      2. Normal vital signs make pneumonia less likely (LR–, 0.18).

      3. The combination of normal vital signs and normal chest exam make pneumonia highly unlikely (sensitivity, 95%; LR–, 0.09).

        image Normal vital signs and a normal lung exam make pneumonia unlikely.

    2. Egophony is fairly specific and significantly increases the likelihood of pneumonia when present (LR+, 8.6).

Table 10-1.Likelihood ratios for physical findings in pneumonia.

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