Case 1: History
The patient is a 54-year-old male who presents with long-standing reddish brown scaly patches and plaques involving his buttocks, lower back, and abdomen.
Microscopic Findings
Sections reveal skin with psoriasiform epidermal hyperplasia and a vaguely bandlike infiltrate of lymphocytes confined mostly to the papillary dermis, which shows fibrosis with wiry bundles of collagen ( Fig. 18.1 ). Epidermal lymphocytes have enlarged, hyperchromatic, and hyperconvoluted nuclei. Accompanying vacuolar change or spongiosis is minimal.
Diagnosis
Mycosis Fungoides
Clinical Presentation
Mycosis fungoides (MF) affects any age group but most commonly presents in adults. Although the spectrum of MF is protean, classic clinical morphology consists of scaly erythematous patches and plaques preferentially involving sun-protected sites. , Patches do not show induration and are simply erythematous and scaly, whereas plaques exhibit indurated texture, which reflects a deeper and denser infiltrate with reticular dermal involvement. Tumors of MF present in nodular fashion. The temporal relationship between patch, plaque, and tumor involvement can vary greatly. Many patients develop protracted patch stage involvement and do not show progression to plaques or tumors.
Histopathology
The histopathologic appearance of MF can also vary. Patch stage MF presents as a bandlike infiltrate of lymphocytes in a fibrotic papillary dermis with wiry collagen. The lymphocytes show nucleomegaly with hyperchromasia and hyperchromatism. Importantly, these lymphocytes are distributed within the epidermis either as single cells or in small groupings (Pautrier collections). The epidermis shows minimal spongiosis or vacuolar change, which can be important in distinguishing MF from dermatitis.
Under a microscope, plaque MF typically includes an infiltrate with reticular dermal involvement. Epidermotropism is also present. In tumors of MF, a dense infiltrate expands and fills the reticular dermis and may also involve the superficial subcutis. Epidermotropism may or may not be evident in the tumor stage.
The immunophenotype of MF most commonly includes coexpression of CD3 and CD4. Some examples of MF express CD8 rather than CD4; for example, a CD8+ immunophenotype is quite common in conjunction with hypopigmented MF. Loss of expression of core T-cell antigens, such as CD7 or CD5, can sometimes be used as an ancillary diagnostic tool. CD30 expression is variable and may be seen with and without large cell transformation (discussed below).
Large cell transformation of MF is defined by the presence of large lymphocytes (three to five times normal) that make up more than 25% of the total infiltrate. Associated CD30 expression is common but it not a diagnostic requirement, and CD30 expression alone does not designate large cell transformation (by definition, this is a cytomorphologic designation). Large cell transformation is most common in late plaque or tumor involvement and signals a risk for a more aggressive clinical course.
Differential Diagnosis
The differential diagnosis includes various forms of dermatitis, including spongiotic (eczematous) dermatitis and pityriasis lichenoides ( Table 18.1 ).
| Mycosis Fungoides | Spongiotic Dermatitis | Pityriasis Lichenoides et Varioliformis Acuta | |
|---|---|---|---|
| Patient age | Any age but predominates in adults | Any age | Adults or children |
| Location | Sun-protected sites | Any site | Trunk, preferentially |
| Distribution of the infiltrate | Superficial dermis with epidermotropism | Superficial dermis with exocytosis | Lichenoid |
| Epidermis | Minimal change | Spongiosis | Interface change with parakeratosis |
| Immunophenotype | Coexpression of CD3 and CD4 is common; CD8 expression is common when hypopigmented | Coexpression of CD3 and CD4 is common | Coexpression of CD3 and CD8 is common |
Spongiotic Dermatitis
Clinical Presentation
Eczematous dermatitis is characterized by the presence of epidermal spongiosis, and additional alterations may be present depending on the entity and duration of the disease. Disorders typified by spongiotic or eczematous epidermal involvement including allergic contact dermatitis, nummular dermatitis, atopic dermatitis, and id reaction. Clinicopathologic correlation is often necessary, as the histopathologic findings of various subtypes are not unique.
Histopathology
Spongiotic dermatitis may present in acute, subacute, or chronic fashion (for examples, see Figs. 3.6 and 3.7 ). The degree of spongiosis tends to diminish with increasing chronicity. Lymphocyte exocytosis into spongiosis and Langerhans cell collections are commonly seen in biopsies of spongiotic dermatitis and represent the most common sources of diagnostic confusion with MF. (Langerhans cell collections, in particular, can be misinterpreted as Pautrier collections.) In spongiotic dermatitis, small lymphocytes show exocytosis into spongiosis, and spongiotic vesicles that include both lymphocytes and Langerhans cells may be found. By contrast, in MF there is epidermotropism of larger atypical lymphocytes with only scant associated spongiosis. Rather than spongiotic vesicles, involvement by MF may include Pautrier collections, which differ from spongiotic vesicles by virtue of their monomorphous cellular content.
Pityriasis Lichenoides
Clinical Presentation
Pityriasis lichenoides et varioliformis acuta (PLEVA) affects a wide age range but is more common in younger patients. PLEVA presents clinically as crops of rounded papules with surface scale. Involvement of the trunk is typical, although involvement of extremities, including acral skin, can sometimes occur. Most cases are asymptomatic.
Histopathology
PLEVA presents microscopically with a lichenoid lymphocytic infiltrate that obscures the dermal–epidermal junction ( Fig. 18.2 ). Associated exocytosis of small lymphocytes and vacuolar change is common, and the epidermis is capped by parakeratosis. There may be associated purpura. Notably, molecular genotyping may reveal associated clonal rearrangement of T-cell receptor genes. There remains debate regarding the significance of T-cell clonality in association with PLEVA. Some authorities interpret the finding as purely incidental, similar to the finding of incidental clonality in association with lichen planus. Others have interpreted the finding as an indication that PLEVA can progress or transform to MF.
Case 2 History
The patient is a 13-year-old Hispanic female with enlarging hypopigmented plaques on the shoulder and back.
Microscopic Findings
Microscopic sections reveal a superficial infiltrate of hyperchromatic hyperconvoluted lymphocytes mostly along the basilar epithelium. The epidermis shows minimal alteration. Immunostaining demonstrates a predominance of T cells expressing CD8.
Diagnosis
Hypopigmented Mycosis Fungoides
Clinical Presentation
In hypopigmented MF, patients develop hypopigmented patches and plaques in non–sun-exposed sites. This variant preferentially involves young patients with skin of color. Hypopigmented MF can also present in patients with fair skin yet may be clinically subtle.
Histopathology
The histopathologic findings of hypopigmented MF are identical to those of conventional MF. Most examples of hypopigmented MF present as patch stage disease. CD8 expression is typical.
Differential Diagnosis
The differential diagnosis includes vitiligo ( Table 18.2 ).
| Hypopigmented Mycosis Fungoides | Vitiligo | |
|---|---|---|
| Clinical appearance | Hypopigmented patches and plaques | Hypopigmented macules and patches |
| Histopathologic features | Epidermotropism by hyperchromatic hyperconvoluted lymphocytes | Reduced melanocyte density and reduced pigmentation with a sparse infiltrate |
| Immunophenotype | Coexpression of CD3 and CD8, commonly | CD8+ lymphocytes can be found in early disease |
Vitiligo
Clinical Presentation
In its inflammatory phase, vitiligo presents as erythematous hypopigmented macules and patches with occasional scale. Late involvement consists of circumscribed areas of depigmentation.
Histopathology
Early vitiligo can include inflammatory cells distributed along the junction. Fully developed vitiligo tends to be hypoinflammatory. Melanocytes are markedly reduced in density or are absent. The reduction in melanocytes coincides with reduced pigmentation of keratinocytes. There may accompanying melanophages in the perijunctional dermis.
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Hypopigmented MF preferentially affects younger patients with skin of color
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The infiltrate of hypopigmented MF includes CD8+ T cells
Case 3 History
A 32-year-old female presents with scattered papules on the trunk and upper right arm. She describes a similar episode a few years ago. Spontaneous resolution was noted.
Microscopic Findings
Sections show a wedge-shaped dermal infiltrate that includes enlarged lymphocytes with vesicular nuclei and prominent nucleoli ( Fig. 18.3 ). Large lymphocytes are mixed with small lymphocytes, histiocytes, and granulocytes in the dermis. CD30 preferentially labels enlarged lymphocytes.
Diagnosis
Lymphomatoid Papulosis, Type A
Clinical Presentation
The clinical course of lymphomatoid papulosis (LyP) is characterized by crops of papules and nodules that undergo spontaneous resolution over a period of weeks. Individual papules are typically smaller than 1 cm and are distributed on the trunk and extremities. The diagnosis of LyP requires identification of key histopathologic features together with a characteristic clinical course. Many patients with LyP are documented to have other forms of lymphoma at some point during their lifetime. Concomitant MF is common, and Hodgkin lymphoma that predates or postdates the onset of LyP may also be observed.
Histopathology
There has been an explosion of LyP subtypes reported in the literature. Classic involvement is referred to as type A; MF-like epidermal involvement is referred to as type B, oligonodular involvement is referred to as type C ( Fig. 18.4 ), cytotoxic LyP with CD8 expression is referred to as type D 7 , and vasculitis-like LyP with angiocentricity is referred to as type E. With the possible exception of type B, most subtypes of LyP include large CD30+ lymphocytes. Subtypes are not mutually exclusive; for example, LyP may present with mixed attributes of subtypes C and D.
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