Codification and Classification

Historically, Langerhans cell histiocytosis includes several clinical syndromes: unifocal disease (including solitary eosinophilic granuloma and Hashimoto-Pritzker, a variant of cutaneous LCH), multifocal single-system disease (including Hand-Schueller-Christian syndrome), and multifocal multisystem disease (including (Abt-)Letterer-Siwe syndrome). The formerly used terms are sometimes useful because they tend to correspond to distinct clinical profiles of LCH , even if the extension of the disease may change during time, leading to difficulties in applying this classification.

However, the international classification of diseases in its versions 9 and 10 – has kept this definition, even if the delimitation between (Abt-)Letterer-Siwe syndrome and other forms of LCH is sometimes difficult. In the international classification of diseases, usually two codes are used, one for the severe and multisystemic form of the disease – sometimes named (Abt-)Letterer-Siwe and sometimes malignant histiocytosis. This represents an ambiguous termination, one presentation of the disease close to a frank cancer and a separate one for the other form(s) of the disease. ICD 9 uses the two codes 202.5 and 277.89. In the ICD 10, the two codes are C 96.0 and D 76.0. Langerhans cell histiocytosis can also be found in the classification of diseases for oncology with the codes M9751/1 and M9752/3. Again it is possible to find a certain ambiguity as the digit after the “/” indicates, if the disease is benign or a frank cancer.

Despite the severity of the presentation of the disease with hematological dysfunction, the clonality of the disease remains controversial and usually, even for the most aggressive presentation of the disease, it is not accepted to consider LCH as a cancer.

Underlining the difficulty to classify this disease, it is also possible to find LCH in the catalogue of Mendelian diseases OMIN, even if there is no obvious pattern of transmissibility of the disease (code 604856) and finally in the Mesh catalogue code (code D006646).

The current Histiocyte Society classification of LCH divides the disease into three groups: unifocal, multifocal unisystem, and multifocal multisystem.