What makes pneumonia atypical?

• A. Caused by bacteria with typical cell walls that respond to penicillin.
• B. Always presents with dense lobar consolidation.
• C. Caused by organisms lacking traditional cell walls, leading to milder symptoms and patchy chest X-ray.
• D. Only affects the elderly.

Answer: (C)

Atypical pneumonia is defined by the type of organisms causing it and how that translates into symptoms and imaging. Organisms that commonly cause it, such as Mycoplasma, often lack a traditional bacterial cell wall. This influences the inflammatory response, so patients tend to have milder, more insidious symptoms, and the chest X-ray shows patchy, diffuse interstitial or bronchopneumonia patterns rather than a single dense lobar consolidation. The absence of a typical cell wall also helps explain why these pathogens are less susceptible to penicillin-class antibiotics. In contrast, pneumonias caused by organisms with a normal cell wall classically produce dense lobar consolidation and can present with more abrupt, intense symptoms. Atypical pneumonia can occur at various ages, not just in the elderly.