Ms. L is a 22-year-old woman who comes to your office in August complaining of cough and fever. She reports that she was in her usual state of health until 3 days ago when a cough developed. Two days ago, a low-grade fever (37.2°C) developed, which increased to 38.8°C yesterday. She reports that her sputum is yellow and that she has no chest pain or shortness of breath.
The framework for the differential diagnosis of acute respiratory complaints is anatomic and microbiologic. Although there are a myriad of viral and bacterial (and occasional mycobacterial) infections that infect the respiratory tree, a practical approach addresses 3 issues:
Where is the infection (sinuses, tracheobronchial tree, alveoli)?
Will the patient benefit from antibiotics?
Among patients with pneumonia, clinicians must separate the common community-acquired pneumonias (CAPs) from the less common but important pneumonias due to aspiration, tuberculosis (TB), and opportunistic infections. Diagnostic and treatment algorithms that summarize the approach to patients with acute respiratory infections appear at the end of the chapter. (see Figures 9–3 and 9–4)
Diagnostic approach: acute cough and fever.
Response to the results of the CXR in patients with cough and fever.
Differential Diagnosis of Acute Coughand Congestion
Opportunistic (eg, Pneumocystis jiroveci pneumonia [PCP])
On physical exam, Ms. L is in no acute distress. Vital signs are RR, 18 breaths per minute; BP, 110/72 mm Hg; pulse, 92 bpm; temperature, 38.6°C. Pharynx is unremarkable; lung exam reveals normal breath sounds without crackles, dullness, bronchophony, or egophony.
|At this point, what is the leading hypothesis, what are the active alternatives, and is there a must not miss diagnosis? Given this differential diagnosis, what tests should be ordered?|
The differential diagnosis for Ms. L includes acute bronchitis, influenza, aspiration pneumonia, and CAP. Ms. L's high fever is a pivotal feature of this case. Acute bronchitis is not usually associated with significant fever (unless caused by influenza). Influenza can cause high fevers and chest symptoms but almost always occurs between December and May. Therefore, despite Ms. L's normal lung exam, the high fever raises the possibility of CAP and makes this the leading diagnosis. Table 9–1 lists the differential diagnosis.
Table 9–1. Diagnostic Hypotheses for MS. L.
| Save Table
Table 9–1. Diagnostic Hypotheses for MS. L.
|Diagnostic Hypothesis||Clinical Clues||Important Tests|
Shortness of breath
Crackles or dullness on lung exam
Sputum Gram stain and culture (occasionally)
|Active Alternatives-Most Common|
Absence of high fever
Normal lung exam
|Chest radiograph (if abnormal lung exam, dyspnea or high fever)|
Severe myalgias December to May
Diagnosis is usually clinical;
Direct immunofluorescence or ELISA can be used
|Aspiration pneumonia||Impaired mentation (dementia, prior stroke, substance abuse)||Chest radiograph|
|Influenza occurs from December to May in the northern hemisphere; it is highly unlikely at other times.|
Ms. L reports drinking only an occasional glass of wine and denies recent intoxication, loss of consciousness, or substance abuse. She reports no travel history and no sick contacts.
|Is the clinical information sufficient to make a diagnosis of CAP? If not, what other information do you need?|
Productive cough and fever are often the presenting symptoms in patients with pneumonia. Symptoms may worsen over days or develop abruptly. Pleuritic chest pain, shortness of breath, chills, and rigors may also develop.
Most common cause of infectious death in the United States
Most common identified pathogens
More common in younger patients
Cannot be distinguished from other pyogenic infections based on clinical presentation or chest radiograph
Influenza (and other viruses)
Staphylococcus aureus infection may develop post influenza.
3.4% of pneumonias are associated with underlying malignancy
Empyema (See Chapter 8, Chest Pain)
Prognosis is good overall.
8% hospitalization rate
95% radiographic cure in 1 month
Diagnosis of pneumonia
Diagnosis is usually clinical, based on constellation of cough, fever, and infiltrate on chest film
Prevalence of symptoms in patients with pneumonia
Fever, 81% but 53% in the elderly
Elderly patients with pneumonia often do not have a fever. Clinicians should have a low threshold for obtaining a chest radiograph in elderly patients or in patients with COPD with cough or with mental status changes.
Pleuritic chest pain, 37–50%
No single finding is very sensitive. Therefore, the absence of any single finding does not rule out pneumonia (Table 9–2).
Neither a normal lung exam nor the absence of fever rule out pneumonia (LR–, 0.6 and 0.8, respectively).
A normal lung exam does not rule out pneumonia.
Normal vital signs make pneumonia less likely (LR 0.18).
Combination of normal vital signs and normal chest exam make pneumonia highly unlikely (95% sensitive, LR 0.09).
Egophony is fairly specific and significantly increases the likelihood of pneumonia when present (LR+ 8.6).
WBC > 10,400 cells/mcL: LR+, 3.7; LR−, 0.6
Sensitivity is lower in dehydrated patients.
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