Mycosis fungoides, plaque vs. Histiocytosis X, plaque

Differential Diagnosis

Mycosis fungoides, plaque Histiocytosis X, plaque 1. Scale-crusts uncommon 1. Scale-crusts common 2. No neutrophils in the epidermis 2. Many neutrophils in the epidermis often 3. Abnormal mononuclear cells in collections in the epidermis appear to be rather cohesive because of scant cytoplasm 3. Abnormal mononuclear cells in collections within the epidermis do not seem to be cohesive because of abundant cytoplasm 4. Abnormal cells in the epidermis sometimes larger than those in the dermis 4. Abnormal cells in the epidermis and dermis of about equal size 5. Abnormal cells sometimes aligned as solitary units in the basal layer of the epidermis 5. Abnormal cells not aligned in the basal layer 6. Infiltrate does not obscure completely the interface between epidermis and dermis 6. Infiltrate often obscures completely the interface between epidermis and dermis 7. Abnormal cells have hyperchromatic and sometimes pleomorphic nuclei 7. Abnormal cells have pale, rather monomorphic nuclei 8. Some nuclei of abnormal cells have a convoluted/cerebriform outline 8. Some nuclei of abnormal cells have a bean- or kidney-shaped (reniform) outline; some of them may be convoluted or cerebriform 9. Abnormal cells have scant azurophilic cytoplasm 9. Abnormal cells have abundant, pale, eosinophilic or amphophilic cytoplasm 10. No multinucleate lymphocytes as a rule 10. Abnormal cells sometimes multinucleate 11. No edema in the upper part of the dermis 11. Edema in the upper part of the dermis sometimes prominent 12. Few, if any, plasma cells in the dermal infiltrate 12. Many plasma cells in the dermal infiltrate often 13. No phagocytosis by atypical cells 13. Phagocytosis by atypical cells 14. Few, if any, extravasated erythrocytes 14. Many extravasated erythrocytes 15. Coarse bundles of collagen in haphazard array in conjunction with patchy lichenoid infiltrates of lymphocytes in the thickened papillary dermis 15. No alteration in bundles of collagen in the upper part of the dermis

Discussion

Plaques of mycosis fungoides and of histiocytosis X have several attributes histopathologic in common, among them epitheliotropism of abnormal mononuclear cells both as solitary units and in collections, slight spongiosis, acanthosis, bandlike infiltrates of cells in the upper part of the dermis, and infiltrates of those cells around at least the venules of the superficial plexus. Plaques of both diseases may consist of mixed-cell infiltrates in which there are eosinophils. Some atypical mononuclear cells may have a convoluted or cerebriform nucleus. In mycosis fungoides, the abnormal cells are lymphocytes, whereas in histiocytosis X they are Langerhans' cells. Lymphocytes have dark nuclei and scant cytoplasm, in contrast with Langerhans' cells, which have pale nuclei and abundant cytoplasm. In mycosis fungoides, the nuclei are not kidney-shaped, whereas in histiocytosis X they often are reniform. In mycosis fungoides, nuclei of abnormal lymphocytes often are larger in the epidermis than they are in the dermis, and tend to be aligned as solitary units in the basal layer. In the upper part of the dermis of longstanding plaques of mycosis fungoides, coarse bundles of collagen are arrayed haphazardly in conjunction with patchy lichenoid infiltrates of lymphocytes. In mycosis fungoides, unlike the situation in histiocytosis X, neutrophils, plasma cells, and extravasated erythrocytes are not usually present in the infiltrate, and there is no edema.

Mycosis fungoides may evolve clinically through patch, plaque, nodular, and tumorous stages, but, in the vast majority of patients, patches monopolize and they remain patches, or progress only to subtly elevated plaques, for a lifetime. Those patients never die of mycosis fungoides; only patients who have formidable plaques, nodules, and tumors do. Plaques may be solitary (e.g., Woringer-Kolopp syndrome) or numerous and widespread. Although patches, plaques, papules, nodules, and tumors may be present at the same time in the same patient, many patients with mycosis fungoides may present themselves with a single patch, usually on a thigh or a buttock, i.e., parapsoriasis en plaques. That may be the only lesion they ever develop. Plaques of mycosis fungoides in persons with light colored skin have a characteristic rust-orange hue. The lesions usually are slightly scaly. Sections of tissue of biopsy specimens from plaques of mycosis fungoides show many atypical lymphocytes, arranged singly and sometimes in collections, in an epidermis that exhibits scant spongiosis.

Patches and subtle plaques of mycosis fungoides display infiltrates composed almost wholly of lymphocytes. Only in longstanding plaques marked by a moderately dense lichenoid infiltrate do eosinophils begin to appear. Plaques may remain plaques, evolve into nodules and tumors, or regress as atrophic patches, i.e., poikiloderma atrophicans vasculare.

Histiocytosis X is a term applied to a spectrum of conditions that are related by virtue of the presence of abnormal cells, which are seen by electron microscopy to contain Langerhans' cell granules in their cytoplasm. Immunoperoxidase stains on fresh frozen tissue with antibodies directed against Langerhans' cell antigens, CD1a (Leu 6, OKT6) are positive in cases of histiocytosis X and negative in mycosis fungoides, as also is the case for S-100 protein. Moreover, the neoplastic lymphocytes of mycosis fungoides stain with antibodies directed against leukocyte common antigen (on formalin-fixed, paraplast-embedded tissue or fresh frozen tissue), pan-T-cell antigens (on fresh frozen tissue only), and T-helper antigens (on fresh frozen tissue only), whereas the neoplastic cells of histiocytosis X are negative with these antibodies.

Letterer-Siwe disease, Hand-Schüller-Christian disease, and eosinophilic granuloma are names given to different manifestations clinical of infiltration by neoplastic Langerhans' cells. Of course there are differences among those conditions in terms of distribution of the infiltrates, but the denominator in common is abnormal Langerhans' cells. Letterer-Siwe disease is the most serious of the three, affecting infants with both cutaneous and internal organ involvement. Yellow-brown, often hemorrhagic papules are present usually on the head, neck, and trunk. Hepatosplenomegaly commonly accompanies the changes cutaneous. In Hand-Schüller-Christian disease, bony infiltration is the most common finding, but one-third of patients with that malady have involvement cutaneous in the form of an oozing, scaly eruption, what often affects the vulva. Fewer patients have a fatal outcome from Hand-Schüller-Christian disease than from Letterer-Siwe disease. Eosinophilic granuloma typically consists of a solitary lesion in a bone; hardly ever is the skin involved, and the disease almost never is fatal.

In short, mycosis fungoides is a malignant neoplasm of lymphocytes (a lymphoma), and histiocytosis X is a malignant neoplasm of Langerhans' cells. The two have findings histopathologic in common, but can be distinguished from each other by application of the criteria set forth here.

Ref:

Differential Diagnosis In Dermatopathology I, Ii, Iii, Iv.chm