Pseudolymphomas

Last Updated: 2020-08-11

Author(s): Anzengruber, Navarini

Pseudolymphom, Cutaneous pseudolymphoma.

Benign lymphocytic proliferation of the skin, which can clinically and histologically mimic malignant lymphoma.

The differentiation between B- and T-cell pseudo-lymphomas is done by immunophenotyping.

Important differentiation between benign and malignant entity is characterized by clinical features and course of the disease.

1. B-cell pseudolymphomas (lymphadenosis cutis benigna, cutaneous inflammatory pseudotumour)

2. Combined B- and T-cell pseudolymphomas (lymphocytic drug reaction)

3. T-cell pseudolymphomas (actinic reticuloid, lymphomatoid contact dermatitis, lymphocytic infiltration of the skin, acral pseudolymphomatous angiokeratoma- APACHE)

4. Non-classifiable pseudolymphomas

Morphological criteria for assignment to an entity varies, e.g. malignant lymphomas can reach deeper into the tissue and have a monomorphic infiltrate. Reactive germinal centres are more likely to be found in pseudolymphomas (lymphocytoma). Furthermore, malignant lymphomas are characterized by a loss of pan-T-cell antigens, such as CD2, CD3 and betaF1. CAVE: follicular lymphoma and cutaneous marginal zone B lymphoma must be distinguished from the MALT type.

There are various causes:

- Drug reaction: Lymphocytic drug reaction 

- Arthropod reaction and idiopathic: lymphadenosis cutis benigna

- Contact allergy: Lymphomatoid Contact allergy 

- Unsolved:

  • Lymphocytic infiltration of the skin
  • Erythema migrans arciforme et palpabile
  • Lymphomatoid papulosis
  • Actinic reticuloid
  • Angiolymphoid hyperplasia with eosinophilia
  • Cutaneous inflammatory pseudotumor
  • Angioimmunblastic cutaneous T-cell lymphoma
  • Other non-classifiable pseudo-lymphomas

Individual, grouped or disseminated papules, nodes or tumours. Diffuse infestation and lymphoadenopathies are more indicative of malignant lymphoma.

  • Clinical features, histology, PCR, southern blot, immunohistochemistry.
  • The expression of monoclonal kappa- or lambda- light chains is in contrast to the polyclonal expression in reactive hyperplasia (pseudolymphoma) generally considered as malignant event. However, B- and T-cell pseudoclones are found in up to 20% of cases of pseudolymphomas.
  • In cutaneous B-cell lymphomas and cutaneous T-cell lymphomas the clonal rearrangement of the Ig chains can be detected either by immunohistochemical analysis with monoclonal antibodies or by immunogenotyping using Southern blot or PCR. The immunohistochemical technique has the advantage of the exact allocation of the antigen in the tissue, but is less sensitive (background staining). Southern blotting can make clonal cells visible in more than 5% of the cells of the lesion; the PCR technique is more sensitive with detection of < 0.1% of clonal cells.

Dense, striped, lymphohistiocytic infiltrate, cell polymorphism, epidermal and vascular involvement. Pleomorphism, hyperchromasia or mitosis may be signs of malignancy, but are rare.

Transition to malignant lymphoma. 

Favourable (monitoring of the clinical course and ensuring that there is no metastasis).

Treatment of the underlying disease, if known, see each case.

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