Hypersensitivity pneumonitis and squawks
In one sentenceA squawk is a short, musical inspiratory sound. It suggests that small airway involvement accompanies a fibrotic pattern.
- Squawk: often a short click first, then a short musical tail. It is inspiratory.
- It is rare. It is informative when heard together with a fibrotic or small airway pattern.
- It is not specific to HP. Interpret it together with the exposure history and HRCT.
Yes. Small airways vibrate briefly as they open, and a squawk arises. Airways that open late also produce crackles.
Not the main change.
Not the main change.
Short inspiratory squawks among fine crackles.
For the reasoning: Where does sound come from? · How does sound reach the chest wall? · How do adventitious sounds arise? · From sound to differential diagnosis
What do you hear?
In inspiration, among fine crackles, you hear a short, chirping musical sound. A crackle-like click often comes just before it. It is shorter than a wheeze and belongs to inspiration.
Why does it sound like this?
The most plausible explanation is as follows. A small peripheral airway suddenly opens or changes shape, and this produces the click. The wall then vibrates briefly while inspiratory airflow continues, and this gives the musical tail. Stiff surrounding lung makes this vibration easier. This sequence has not been shown directly in living patients.
Where is it heard?
The classic setting is hypersensitivity pneumonitis. It is also heard in connective tissue disease, bronchiolitis, fibrosis related to microaspiration and other interstitial diseases. Outside ILD, a recognised setting is pneumonia.
Distinguishing clues
- Link with imaging: Squawks are associated with mosaic attenuation, which points to small airway heterogeneity.
- Context: When exposure to birds, mould or damp, physiology and HRCT all point the same way, a squawk adds weight to that direction.
A squawk does not identify a single diagnosis. What it does is raise the likelihood that peripheral airway involvement is contributing to the interstitial process.
Next step
Take a detailed exposure history: birds, feathers, mould, damp surroundings. On HRCT, look for mosaic attenuation and air trapping. If needed, plan bronchoalveolar lavage (BAL).
Try this pattern in a case
Going deeperresidents · specialists · numbers and sources
Duration and definition
CORSA defines a squawk as a relatively short inspiratory musical sound that often begins with a crackle. According to CORSA, a squawk rarely lasts longer than 400 ms. This duration can overlap with the operational duration criterion for wheeze. So duration alone is not enough to define a squawk. You also need inspiratory timing, a musical quality, a crackle-like onset and the clinical context. The term is not used in the same way in all languages and clinical traditions.
Clinical cohort evidence
In an ILD cohort of 1,000 patients, squawks were seen mainly in fibrosing interstitial diseases with bronchiolar involvement. They were associated with mosaic attenuation. The classic study that described squawks in extrinsic allergic alveolitis (HP) and other pulmonary fibroses is by Earis et al. (1982). Squawks have also been reported in pneumonia (Paciej et al., 2004).
Evidence for the mechanism
The squawk waveform combines a short, non-musical onset with a short oscillating tail. This structure suggests a coupled mechanical sequence rather than an oscillator that runs through the whole breath. Its link with peripheral airway involvement supports a small airway source. What is missing is a direct in vivo demonstration that times a specific airway opening against the recorded squawk.
See the reference list for sources.