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B-cell pseudolymphoma – regarded as a distinct clinical entity
| • | (idiopathic) lymphocytoma cutis |
| • | borrelial lymphocytoma cutis |
T-cell pseudolymphoma – a heterogeneous group of diseases rather than a diagnosis sui generis;
| • | +/- LyP (= “a T-cell infiltrate of unpredictable behavior”) |
B-cell = nodular
T-cell = two patterns
band-like (major pattern) AKA MF-like
| • | lymphomatoid drug eruptions (most) |
nodular (minor pattern)
| • | persistent bite reaction (most) |
mnemonic:
| • | A,A is nodular (type A LyP and arthropod bite) |
| • | B,C and D are band-like (type B LyP, CAD, drug) |
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Cutaneous T-cell Pseudolymphoma:
| • | as in most cases of CTCL, the lymphocytes in CTPL are CD4+ |
| • | exception = actinic reticuloid (CD8+) |
| • | loss of pan-T-cell markers (CD2, CD3, CD5) described in CTCL, has not been reported in CTPL |
| • | loss of CD7, common in CTCL, is rare in CTPL |
Cutaneous B-cell Pseudolymphoma:
| • | one predominates (>10:1 or <0.5:1) in CBCL |
| • | monoclonal antibodies to bcl-2 protein and MT2 are useful markers in distinguishing primary cutaneous follicular lymphomas from CBPL with germinal centers: |
bcl-2 protein:
| • | a proto-oncogene; blocks apoptosis |
| • | rarely seen in pseudolymphoma with germinal centers |
MT2-CD45RA:
| • | = an IgG antibody that reacts with antigens on both T and B lymphocytes of the mantle and marginal zone |
| • | expression is exclusively restricted to follicular lymphomas (i.e. specific) |
| • | low sensitivity (≈ 20%) therefore negative results do not exclude a malignant process |
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