[Histiocytosis X. Problems of differential diagnosis in adults]

A now 20-year-old man has been suffering from diabetes insipidus for four years. Two years ago a tumour in the hypophyseal stalk-hypothalamus region had been removed, but no definitive histological diagnosis could be established. When aged 19 he developed cutaneous changes which for the first time led to histiocytosis being suspected. Also for the first time, multiple small foci were noted in both lungs. Histological examination of a transbronchial lung biopsy demonstrated histiocytosis X. No specific treatment is being considered at present, because the patient is symptom-free and has normal lung function.