Lymphocytic interstitial pneumonitis

Lymphocytic interstitial pneumonitis (LIP) is a benign lymphoproliferative disorder characterised by lymphocyte predominant infiltration of the lungs ^1,5. It is classified as a subtype of interstitial lung disease.  It also falls under the umbrella of non lymphomatous pulmonary lymphoid disorders ⁷.

Demographics and clinical presentation

There is a recognised female predilection.

Pathology 

There is generally diffuse infiltration of the interstitium and alveolar spaces by lymphocytes and plasma cells.

Associations

• Sjogren syndrome: can occur in up to 25% of those with LIP ⁶
• AIDS: particularly if it occurs in the young
• rheumatoid arthritis
• auto immune thyroid disease
• systemic lupus erythematosus (SLE)
• Castleman disease

Radiographic features

Chest radiograph

• features can be non specific, but may include
  • lower-zone predominant bilateral reticular opacification
  • chronic bilateral airspace opacification

HRCT

The following features may be seen with LIP on HRCT, but the findings are not exclusive to its diagnosis.

• features generally tend to be diffuse
• mediastinal lymphadenopathy
• ground-glass change
• scattered thin walled cysts - usually deep within the lung parenhyma and range from 1-30 mm (useful for differentiation between lymphoma or the lung ¹)
• intersitital thickening along lymph channels ²
• thickening of bronchovascular bundles
• small but variably sized pulmonary nodules (can be centrilobular or subpleural, and often ill defined)

Treatment and prognosis 

The natural history is variable, from near complete resolution to progressive disease. Corticosteroids have been successfully trialled ¹.

Differential diagnosis

General imaging differential considerations include

• pneumocystis pneumonia (PCP/PJP) - can be difficult to differentiate particularly in those with AIDS