ILD

aka diffuse parenchymal lung diseases

Anatomic

Some are more:

Not all causes fibrosis

Allergic: HP, Eos pna Non-allergic: sarcoidosis, PLCH, ARDS, Alveolar proteinosis, RB-ILD, LAM Functional: aspiration/GERD associated pneumonitis

ILA = interstitial lung abnormality.. basically, an "ILD-nodule". not clear currently if this is "pre-ILD". About 2-10% incidence,

ILD related to primary pulm disorder (e.g. sarcoidosis, PAP, LAM, eosinphilic pneumonia)
ILD related to exposure (pneumoconiosis, HP - use ATSDR))
ILD related to drugs/illicits/radiation (pneumotox)
ILD associated with CTD
and Idiopathic interstitial pneumonias (IIPs) such as IPF

Exposure terminology:

pneumoconiosis occurs following chronic exposure to respirable dust
HP occurs after immune-mediated sensitization to organic/protein antigens. (Old name: "extrinsic allergic alveoli's")
some IIPs are associated with exposures (e.g. IPF)

###For CT interpretation:

Describe in terms of the lobule: size of the lobule =where bronchial vessel ends = ~a few cm

Pattern can be: alveolar, bronchiolocentric (e.g. air trapping in HP, PLH, sarcoid), perivascular (e.g. LAM) or panlobular.

vs centrilobular = not near vessels

###UIP called Idiopathic Pulmonary Fibrosis if there is no identifiable cause.

CT: diffuse peripheral reticular patterns with honeycombing, traction bronchiectasis, basilar

###NSIP

-ground glass opacities or consolidations that mainly involves lower lungs

-subactute onset dyspnea.

alt

HRCT
If HRCT is not diagnostic, BAL and cellular analysis (e.g. eos over 25%, lymphs over 50, 'alveolitis' = neutrophilic, blood, etc.)
if that is not diagnostic: Lung Biopsy (surgical is reference standard, but can consider transbronch / cryo)

For acute course: think COP, AIP (aka Hamman Rich, ARDS), Eos PNa, HP, Drugs (amiodarone, nitrofurantoin)

For CTD related, ANA - IFA is sensitive but not specific, hence reflex.

Source: CHEST 2018; 154(2):394-408

Parenchymal manifestations of smoking: emphysema and ILD.

Causally Related:

RB-ILD (Respiratory Bronchiolitis- ILD). RB = pigmented macrophages in bronchioles and peribronchiole alveoli. May or may not be associated with symptoms. Upper lobe predominant centrilobular micro nodules are the most classic imaging finding (though is on a spectrum with DIP). All active smokers have some of this, and 50% of ex-smokers. Less severe presentation than DIP.
DIP (Desquamative Interstitial Pneumonia) - actually a misnomer, as it is collections of pigmented macrophages and not epithelial cells on path. Smoker in 60-90%, rest can be result of RA/SLE/Sclero/Myositis or exposures to beryllium, copper, tungsten / textile workers. Bilateral, symmetric GGOs in peripheral bases (ddx UIP but more ground glass). Old case series suggest steroids but evidence is very weak. Most severe clinically (restriction, DLCo decrease). In the future, smoking related DIP may get lumped with RBILD and nonsmoking related may get lumped with NSIP (they clinically behave like this)
SRIF (Smoking-Related Interstitial Fibrosis) - newly described. Upper lobe predominant reticulations, emphysema, maybe some GGOs. Path with septal thickening, nonfocal deposition of hyalinzed collagen in the septal walls of alveoli. Also seen in all smokers. Clinical ramifications are not well understood.
PLCH (Pulmonary Langerhan Cell Histiocytosis) - a myeloid neoplasm with inflammatory properties that is induced by cigarette smoke.
Acute Eosinophilic Pneumonia

alt

May be risk factor or trigger for:

IPF
CPFE (combined fibrosis and emphysema) = whenever these co-exist, the natural history changes significantly (poor prognosis). Spirometry is relatively normal, with marked reduction in DLCo
CTD-ILD

Not associated with physiologic abnormality (e.g. PFTs, symptoms), but finding On CT (small area usually)

2-10% prevalence, increased association with mortality - maybe due to being a harbinger for onset of ILD (Not all do)