Histiocytosis X, also known as Langerhans cell histiocytosis, is a disorder in which there is clonal proliferation of the Langerhans cell (an antigen-presenting cell) which results in granulomatous lesions in organs.
Multiple organs can be affected but the commonest affected is bone, followed by skin.
Presentation depends on the organ(s) affected and varies from asymptomatic to swelling and pain, systemic features and organ failure.
Pulmonary histiocytosis is commonest in young smokers. Presentation tends to be with a non-productive cough or dyspnoea. CXR shows upper and mid-zone nodules and reticular/cystic changes.
The characteristic feature on biopsy is Birbeck granules.
Treatment options in problematic disease include surgical excision, steroids, radiotherapy or chemotherapy.
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