AssessmentsPneumonia: Pathology review
USMLE® Step 1 style questions USMLE
A 58-year-old man goes to the emergency department for evaluation of fever and dry cough for the past week. He has also become progressively more dyspneic, and walking a single block makes him short of breath. He underwent a liver transplantation 4-months ago for treatment of autoimmune hepatitis and is currently taking several immunosuppressant drugs. Temperature is 38.5°C (101.3°F), pulse is 104/min, respirations are 20/min, blood pressure is 122/88 mmHg, and oxygen saturation is 89% on room air. Lung auscultation reveals bilateral crackles and rhonchi. Chest radiograph reveals bilateral, diffuse interstitial infiltrates extending from the perihilar region. Leukocyte count is 13,000/mm3 and serum lactate dehydrogenase level is 460 U/L. Further testing is most likely to reveal which of the following findings?
Content Reviewers:Yifan Xiao, MD
Two people came to your clinic one day.
Physical examination reveals fever, tachycardia, and tachypnea. Her lung sounds are barely audible, but it had crackles at the left base.
Next is Jeremy, a 64-year-old man who was hospitalized for a stroke 2 weeks ago.
He recently developed a cough and right-sided chest pain.
He is tachycardic and has a fever of 38.4°C.
Examination reveals fremitus, decreased breath sounds, and dullness to percussion in the right lower lung field.
Chest x-rays were performed which showed a left lower lobe infiltrate in Mariah’s case, and a right lower lobe infiltrate in Jeremy’s.
Now, both people have pneumonia.
So pneumonia is an infection of the lung tissue.
These pathogens then triggers an inflammatory response.
However they can also accumulate in the lungs, filling up the alveoli.
Individuals might also develop pleuritic chest pain, which is characterized by sudden and intense sharp, stabbing, or burning pain in the chest when inhaling and exhaling; and productive cough with yellow sputum.
Besides these, High yield signs that might come up on your exam include dullness to percussion, which suggests that there’s a lung consolidation.
This occurs because the air in the alveoli is replaced by pus and fluid so the sound will lose its normal tympanic or drum-like quality.
There’s also tactile fremitus, which is when you can feel increased vibrations when you place your hand on the individual’s chest or back on the area with the consolidation and they say 99.
Similarly, if you auscultate the area with the consolidation, the “99” will sound louder and this is called bronchophony.
This is because sound waves and vibrations travel better through the fluid-filled consolidated tissue than air-filled healthy tissue.
For a similar reason if you put your stethoscope on the area with the consolidation, you can hear bronchial breath sound where the sound of air moving in the bronchi is transmitted clearly through the consolidated area.
Next is egophony which is increased resonance in the area with consolidation, so when asked to say the “E” it will sound like the letter “A.”
Late inspiratory crackles can also be heard over the affected area.
Now, there are many ways to categorize pneumonia.
One way would be by the causative microbes.
This type usually has an abrupt onset and tends to develop secondary bacterial pneumonia.
“Atypical or walking pneumonia” is also caused by bacteria, but the individual won’t develop the classic symptoms.
Another clue is that it tends to occur in areas with many people packed together like in military recruits training camps and prisons.
This bacteria can be found in water-systems or water-based cooling systems in hotels, which is why this infection is also common in travelers.
The next high yield concept is that people in certain age groups are more at risk for certain types of microbial infections.
In those 4 weeks to 18 years, the condition is typically caused by viruses like the Respiratory syncytial virus, but also by bacteria such as Chlamydia trachomatis, which is more common in those younger than 3, and Chlamydophila pneumoniae, which is usually found in school-aged children.
The last age group is individuals over 40, especially the elderly over 65.
The most frequent causes are Streptococcus pneumoniae, anaerobes, and viruses.
Another special group is people who are immunocompromised.
And finally, in post organ transplant patients who are on immunosuppressants, pneumonia with intranuclear and cytoplasmic inclusion bodies histologically points to opportunistic infection by Cytomegalovirus.
Pneumonia can also be categorized by where it’s acquired.
It tends to be more serious because these individuals often have weakened immune systems and the microbes in hospitals are often resistant to the common antibiotics.
Some high yield bacteria to remember are Methicillin-resistant Staphylococcus aureus or MRSA, which is usually carried by asymptomatic hospital staff; Legionella pneumophila, which can be found in water-systems or water-based cooling systems in hospitals is also common.
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