Lymphoid interstitial pneumonia (LIP), also known as lymphocytic interstitial pneumonitis, is a benign lymphoproliferative disorder characterised by lymphocyte predominant infiltration of the lungs. It is classified as a subtype of interstitial lung disease. It also falls under the umbrella of non-lymphomatous pulmonary lymphoid disorders.
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Epidemiology
Lymphoid interstitial pneumonia can occur at any age. However, most of the patients are adults with a mean age of 52-56 years. If a child presents with lymphoid interstitial pneumonia, this can be indicative of AIDS.
There is a recognised female predilection (by ~2 fold) most likely attributable to the fact that lymphoid interstitial pneumonia occurs in patients with autoimmune diseases such as Sjögren syndrome, which is by far more common in women 8.
Associations
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considered the most common lung pathology in these patients 14.
can occur in up to 25% of those with lymphoid interstitial pneumonia 6
AIDS: particularly if it occurs in the young 9
Clinical presentation
The main clinical symptoms are a gradual onset of dyspnoea and cough with approximately 6 months duration. Less frequently, patients may have systemic symptoms such as fever, night sweats, arthralgia, and weight loss. If the disease progresses to end-stage respiratory failure, cyanosis and clubbing may develop. Hypertrophy of the salivary glands may be seen in 20% of patients 11.
Pathology
It is considered a benign lymphoproliferative disorder characterised histologically by diffuse interstitial and alveolar infiltration with polyclonal lymphocytes and plasma cells.
Markers
In about 80% of patients polyclonal or IgM monoclonal gammopathy is found 8.
Radiographic features
Plain radiograph
Features can be non-specific, but may include:
lower-zone predominant bilateral reticular opacification
CT
The following features may be seen with lymphoid interstitial pneumonia on HRCT, but the findings are not exclusive to its diagnosis:
features tend to be diffuse with mid to lower lobe predominance
interstitial thickening along lymph channels 2
small but variable-sized pulmonary nodules (can be centrilobular or subpleural, and are often ill-defined)
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scattered thin-walled cysts
usually deep within the lung parenchyma
typically abut vessels (i.e. perivascular or subpleural)
size range between 1-30 mm (useful for differentiation from lymphoma of the lung 1)
Treatment and prognosis
The natural history is variable, from near-complete resolution to progressive disease. More than 30% of patients will develop end-stage disease and honeycombing despite treatment. According to some reports, 5-year mortality can range between 33-50% ref.
Transformation to lymphoma can occur, particularly in a patient with monoclonal gammopathy or hypogammaglobulinemia 8. Corticosteroids have been successfully trialled 1.
Complications
Approximately 5% of cases may transform into lymphoma 15.
History and etymology
It was originally classified as an idiopathic interstitial pneumonia in 1969 by Liebow and Carrington.
Differential diagnosis
General imaging differential considerations include:
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cystic changes (pneumatoceles) seen in advanced disease
can be difficult to differentiate particularly in those with AIDS
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occur in younger females
cysts are generally uniformly distributed throughout the lungs
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smokers
bizarre cysts that spare the costophrenic angles
upper lung zone predominant