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Should benign cephalic histiocytosis be renamed? Let’s keep our heads about this decision.


DII small banner By Warren R. Heymann, MD
Sept. 4, 2017


Benign cephalic histiocytosis (BCH) is a rare non-Langerhans cell histiocytic disorder first recognized by Gianotti 46 years ago. (1) Over the years, I have seen several cases of both Langerhans cell histiocytosis (LCH), and non-Langerhans cell histiocytoses, but do not recall ever having seen BCH.

Before going into detail about BCH, it is appropriate to review the current status of the “histiocytoses”. To date, more than 100 subtypes have been described, and the classification is being reworked. Remember that dendritic cells (DCs), monocytes, and macrophages are within the mononuclear phagocyte system, whereas “histiocyte” is a morphologic term for a tissue-resident macrophage. Macrophages clear debris while DCs present antigens. Human DCs are classified into two types — plasmacytoid and myeloid. Langerhans cells (LCs) are intraepidermal DCs, expressing CD1a and contain Birbeck granules (which positively stain Langerin with CD207).
 
In 1987, the Working Group of the Histiocyte Society classified the histiocytoses in three categories: 1) LC histiocytoses; 2) non-LC histiocytoses; and 3) malignant histiocytoses. Because of advances in molecular pathology, the Histiocyte Society has proposed a new classification:  1) the “L” (Langerhans) group (including LCH, Erdheim-Chester disease and extracutaneous juvenile xanthogranuloma); 2) the “C” group of cutaneous and mucocutaneous histiocytoses (divided into the “xanthogranuloma” family of  BCH,  juvenile xanthogranuloma [JXG], generalized eruptive histiocytosis, xanthoma disseminatum, and progressive nodular histiocytosis, and the “non-JXG” family composed of necrobiotic xanthogranuloma and multicentric reticulohistiocytosis; 3) The “M” group of malignant histiocytoses which may be primary or secondary to other lymphoproliferative malignancies such follicular lymphomas and hairy cell leukemia, amongst others; 4) the “R” group composed of Rosai-Dorfman disease and H syndrome; and 5) the “H” group of hemophagocytic lymphohistiocytosis and macrophage activation syndrome, either of the primary type or secondary to infectious, immune, or malignant disorders. (2)

The reclassification is becoming increasingly important in the molecular era. For example, BRAF mutation status cannot be predicted based on clinical parameters, yet have been shown to be present in approximately half of LCH patients, but not in the other groups. This may have profound therapeutic implications for the use of BRAF inhibitors. (3)

Ekinci et al have published their observations on 11 patients with BCH. There were 5 girls and 6 boys (median age 24 months, range 9-72 months). The median age at the onset of lesions was 8 months (range 3-36 months). The lesions first appeared on the face in 10 patients and on the trunk in one. Proximal parts of the extremities and trunk were also involved in nine patients (81.8%). Patients were categorized into two groups based on their clinical features; five had 20 to 30 predominantly red-brown dome-shaped papules and six had 50 to hundreds of yellow-brown or predominantly pinkish brown flat papules. Four patients were lost to follow-up. In 7 patients with a mean follow-up of 5 years, 4 had nearly complete resolution and 3 showed remarkable regression without treatment. (4)
 
With the exception of rare cases of BCH complicated by diabetes insipidus or diabetes mellitus, the disorder is not associated with systemic manifestations. Mucosal lesions have not been reported. Histologically, lesions are characterized by histiocytes that are CD68+ and negative for CD1a and S-100. (5) Even with a characteristic clinical presentation, biopsies may prove valuable. Haimovic et al reported the case of a 12 month old boy with typical facial lesions and H&E histology consistent with BCH. Immunohistochemical stains, however, were positive for S-100, CD1a, CD68, and Factor XIIIa (and, I presume, negative for CD 207), allowing for a diagnosis of indeterminate cell histiocytosis. (6)  Because most lesions resolve spontaneously, possibly with postinflammatory hyperpigmentation, expectant observation may be the most appropriate management.

In their conclusion, Ekinci et al state: “Because of the extracephalic cutaneous involvement seen in the great majority of our series and in most cases in the literature, the term ‘cephalic’ may merit reevaluation.” I understand their rationale, but I would leave the term BCH alone. As they reported, the overwhelming majority of cases commence on the face, and virtually all patients have facial involvement. There is a precedent for this – unilateral laterothoracic exanthem (ULTE) starts on one side, but commonly progresses over the entire trunk, yet we still call it ULTE. (I tried to think of a better name for BCH, but could not. The best I could do was “shayna punim” histiocytosis [Yiddish for “pretty face”], but that may not be so accurate.) With rapid molecular advances redefining the categorization of the histiocytoses, I believe that it is essential that we maintain comprehensible names that accurately portray a disease process. From that perspective BCH fits the bill — it is benign, involves the head (and beyond), and is a histiocytosis. If you can improve on that, please let me know!

1. Patsatsi A, et al. Benign cephalic histiocytosis: Case report and review of the literature. Pediatr Dermatol 2014; 31: 547-50.
2. Emile JF, et al. Revised classification of histiocytoses and neoplasms of the macrophage-dendritic cell lineages. Blood 2016; 127: 2672-81.
3. Bubolz AM, et al. Potential clinical implications of BRAF mutations in histiocytic proliferations. Oncotarget 2014; 30: 4060-70.
4. Ekinci AP, et al Novel clinical observation on benign cephalic histiocytosis in a large series. Pediatr Dermatol 2017; 34: 392-7.
5. Lange M, et al. Benign cephalic histiocytosis. Cutis 2015; 95: e15-7.
6. Haimovic A, et al. Indeterminate cell histiocytosis that presented clinically as benign cephalic histiocytosis. Dermatol Online J 2014; 20 (12).

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