Histiocytosis
A rare but potentially deadly disorder with similarities to cancer, in which histiocytes start to multiply and attack the person's own tissues or organs.
The result can be tissue damage, pain, development of tumor-like lumps called granulomas, fatigue, and other symptoms.
If histiocytosis affects the pituitary gland, diabetes insipidus may also develop.
Treatment is by radiation and chemotherapy, although for reasons unknown, some cases go into remission without treatment