Pulmonary Langerhans Cell Histiocytosis typically presents in young adults smokers characterised by the presence of Langerhans cells with eosinophilic infiltration in the lung with nodular and cystic changes predominantly in the mid- to upper lung zones.
Description
Pulmonary Langerhans Cell Histiocytosis (PLCH) is an uncommon interstitial lung disease marked by the accumulation of Langerhans cells in the lung interstitium leading to characteristic granulomatous changes. Langerhans cells are dendritic cells that function as antigen-presenting cells. While the disorder primarily affects the lungs, it can also involve other systems, specifically the skin and bones.
Pathogenesis
The pathogenesis of PLCH involves the aberrant accumulation and proliferation of CD1a-positive Langerhans cells in response to cigarette smoke. These cells release cytokines and chemokines, attracting other inflammatory cells and leading to the formation of granulomas. Over time, these granulomas can coalesce and form nodules, which may cavitate to create cysts. Chronic inflammation and fibrosis result in the characteristic radiological features of the disease. Genetic mutations, such as BRAF V600E, have been identified in some cases, suggesting a neoplastic component.
Epidemiology, Risk Factors & Associations
PLCH primarily affects adults, with the majority of patients diagnosed between the ages of 20 and 40. It is estimated to occur in 1 in 1,000,000 individuals annually. The primary risk factor for PLCH is smoking, with up to 90% of patients being smokers. It is occasionally seen in non-smokers, and there is a higher prevalence in females.
Clinical Features
- The most common symptoms are non-productive cough, dyspnoea, and chest pain.
- Systemic features such as weight loss and fatigue are present in a minority of cases.
- Clubbing is present in 20-50% of patients.
- Spontaneous pneumothorax can occur in up to 15-20% of cases.
Complications
- Progressive respiratory failure
- Spontaneous pneumothorax
- Pulmonary hypertension
Subtypes
As an isolated disorder, PLCH does not have specific subtypes, although the severity and course of the disease can vary among individuals.
Pathological Features
Histopathology
- Macroscopic: Multiple small nodules and cysts, predominantly in the upper lobes.
- Microscopic: The presence of Langerhans cells with grooved nuclei and abundant eosinophilic cytoplasm is a key feature. Nodular infiltrates of Langerhans cells (CD1a-positive, S-100 positive). Presence of eosinophils, lymphocytes, and plasma cells. Birbeck granules visible on electron microscopy. Fibrosis and cavitation in advanced stages.
Serology
- Elevated inflammatory markers (e.g., C-reactive protein) in active disease.
- Testing for BRAF V600E mutation can be helpful in some cases.
Biochemistry
- Routine biochemistry typically unremarkable unless associated with other systemic involvement.
Immunohistochemistry
- Immunohistochemistry often reveals Langerhans cells to be positive for S100 and CD1a.
Radiological Features
General Features
The radiological appearances of PLCH are distinctive and characteristically show nodules and cysts in a predominantly upper and mid-zone distribution.
XR
- Diffuse bilateral parenchymal reticulnodular pattern with relative lower zone sparing
- Cystic changes may be seen
- Static lung volumes are preserved
CT
- Characteristic presence of peribronchiolar nodules which cavitate into cysts in the upper and middle lung zones with sparing of the costophrenic angles.
- As cysts conglomerate, they form irregular morphology: irregular, cloverleaf or bizarre shapes
- Honeycomb lung, term describing multiple small cysts
- Cysts can have thick or thin walls.
- Lung volumes are preserved
Grading and Staging
Currently, there’s no established grading or staging system for PLCH. The clinical course is variable, ranging from spontaneous remission to progressive respiratory failure.
Diagnosis
A definitive diagnosis of PLCH relies on histopathological examination, typically from lung biopsy showing CD1a-positive Langerhans cells and Birbeck granules.
Differential Diagnosis
- Sarcoidosis: Can present with similar lung nodules, although these are typically randomly distributed and associated with mediastinal lymphadenopathy.
- Lymphangioleiomyomatosis (LAM): Similar cystic changes but usually occurs in younger women and associated with tuberous sclerosis.
- Emphysema: Smoking related disease. Shows upper lobe predominant cystic changes, but these are not true cysts with imperceptible thin walls and demonstrate a central dot sign representing the centrilobular artery.
Management
- Management primarily involves smoking cessation, which can lead to a halt in disease progression and even improvement in lung function in many cases.
- For progressive disease, corticosteroids may be used, although their effectiveness is not definitively established. Referral to a respiratory specialist for further management, including lung transplantation in severe cases, may be necessary.
- The diagnostic approach typically involves a combination of radiological assessment and lung biopsy for histopathological confirmation.