Langerhans Cell Histiocytosis
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Direct answer
Langerhans cell histiocytosis is a clonal proliferation of CD1a and langerin positive dendritic cells, roughly half carrying a BRAF V600E mutation, that may be unifocal or multisystem. Birbeck granules on electron microscopy, together with CD1a and S100 positivity on immunohistochemistry, confirm the diagnosis. Infants often show a scaly, seborrhoeic-like rash in the scalp and napkin area, and treatment ranges from local therapy for limited disease to chemotherapy for multisystem disease.
What you must remember
- Cell markers: CD1a and langerin (CD207) positive Langerhans cells, with S100 positivity; the cells are large with grooved or folded nuclei and eosinophils are present.
- Birbeck granules: rod-shaped or tennis-racquet-shaped cytoplasmic organelles seen on electron microscopy, linked to langerin.
- Mutations: BRAF V600E in roughly half of cases, activating the MAPK pathway, with other MAPK-pathway mutations described.
- Disease types: single-system unifocal disease such as a solitary bone lesion, multifocal unisystem disease, and multisystem disease.
- Letterer-Siwe disease: acute, disseminated disease in infants with a poor prognosis, often with skin and visceral involvement.
- Hand-Schuller-Christian disease: chronic disease with the classic triad of skull lesions, exophthalmos and diabetes insipidus.
- Cutaneous features: seborrhoeic-like scaly papules in the scalp, flexures and napkin area, purpuric papules, and gingival disease with bone loss in adults.
- Treatment: local steroids or excision for limited disease, vinblastine with prednisolone for multisystem disease, and BRAF inhibitors such as vemurafenib in refractory cases.
From a scaly infant rash to the extent of disease
Langerhans cell histiocytosis mimics seborrhoeic dermatitis or scabies in infants, so biopsy is essential when the rash is persistent. The steps below move from the rash to the extent of disease.
- Recognise the rash: persistent, scaly, seborrhoeic-like papules on the scalp, flexures and napkin area, sometimes with purpura.
- Biopsy the lesion: a biopsy shows infiltration by Langerhans cells with grooved nuclei admixed with eosinophils.
- Stain and examine: CD1a and langerin positivity confirm the lineage, and electron microscopy shows Birbeck granules.
- Check BRAF status: BRAF V600E testing guides targeted therapy if disease is refractory.
- Survey the organs: a full blood count, liver and renal function, chest imaging and a skeletal survey look for organ and bone involvement.
- Assess risk organs: involvement of the liver, spleen, lungs or haematopoietic system predicts a worse course and calls for systemic therapy.
- Choose therapy by extent: local steroids or excision for unifocal disease, vinblastine with prednisolone for multisystem disease, and BRAF inhibitors in refractory cases.
Where the exam tries to catch you
Langerhans cell histiocytosis is easy to dismiss as dermatitis in infants and is often confused with its named syndromes.
- Trap: calling an infant's scaly scalp and napkin rash seborrhoeic dermatitis without biopsy. Correct: a persistent, widespread or purpuric rash that resists topical therapy warrants biopsy for Langerhans cell histiocytosis.
- Trap: equating Hand-Schuller-Christian disease with Letterer-Siwe disease. Correct: Letterer-Siwe is acute and disseminated in infants, whereas Hand-Schuller-Christian is chronic with the classic triad.
- Trap: forgetting the ultrastructural clue. Correct: Birbeck granules are rod-shaped or tennis-racquet structures on electron microscopy, and CD1a with langerin supports them.
- Trap: using systemic chemotherapy for a single bone lesion. Correct: unifocal disease is treated locally, and systemic chemotherapy is reserved for multisystem disease.
Frequently asked questions
What are Birbeck granules in Langerhans cell histiocytosis?
Birbeck granules are rod-shaped or tennis-racquet-shaped cytoplasmic organelles seen on electron microscopy in Langerhans cell histiocytosis. They are linked to langerin (CD207), so langerin positivity supports the diagnosis when Birbeck granules are not visible.
What distinguishes Letterer-Siwe disease from Hand-Schuller-Christian disease?
Letterer-Siwe disease is an acute, disseminated form that affects infants and carries a poor prognosis. Hand-Schuller-Christian disease is a chronic form in older children with a classic triad of skull lesions, exophthalmos and diabetes insipidus.
Which mutation is commonly found in Langerhans cell histiocytosis?
BRAF V600E is found in roughly half of Langerhans cell histiocytosis cases, activating the MAPK pathway. The mutation matters for treatment, because BRAF inhibitors such as vemurafenib can be used in refractory disease.
Why is Langerhans cell histiocytosis a concern in infants with seborrhoeic-like rashes?
Langerhans cell histiocytosis can present as a scaly, seborrhoeic-like rash in the scalp and napkin area of infants, mimicking common dermatitis. A persistent or purpuric rash that resists topical therapy should prompt biopsy and systemic assessment.
What is the treatment for unifocal Langerhans cell histiocytosis?
Unifocal Langerhans cell histiocytosis, such as a solitary bone lesion or limited skin disease, is usually treated locally with curettage, intralesional steroids or excision. Systemic chemotherapy with vinblastine and prednisolone is reserved for multisystem disease.