Pseudolymphomas

Pseudolymphoma, Cutaneous pseudolymphoma,

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

Distinguishing between B- and T-cell pseudolymphomas is done using immunophenotyping.

Important distinction between benign and malignant entity is characterised by clinic and course of 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. Unclassifiable pseudolymphomas

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

There are various causes:

- Drug reaction: Lymphocytic drug reaction

- Arthropod reaction and idiopathic: Lymphadenosis cutis benigna

- Contact allergy: Lymphomatoid contact allergy

- Unexplained:

• Lymphocytic infiltration of the skin
• Erythema migrans arciforme et palpabile
• Lymphomatoid papulosis
• Actinic reticuloid
• Angiolymphoid hyperplasia with eosinophilia
• Cutaneous inflammatory pseudotumour
• Angioimmunoblastic cutaneous T-cell lymphoma
• Other unclassifiable pseudolymphoma

Single, grouped or disseminated papules, nodules or tumours. Diffuse involvement and lymphoadenopathies are more indicative of malignant lymphoma

• Clinical, histology, PCR, Southern blot, immunohistochemistry.
• In contrast to polyclonal expression, the expression of monoclonal kappa or lambda light chains in reactive hyperplasia (pseudolymphoma) is generally considered malignant. However, B- and T-cell pseudoclones are encountered in up to 20% of cases of pseudolymphoma
• In cutaneous B-cell lymphomas and cutaneous T-cell lymphomas, clonal rearrangement of 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 exact assignment of the antigen in the tissue, but is less sensitive (background staining). By Southern blotting, clonal cells can be visualised in more than 5% of the cells of the lesion; the PCR technique is more sensitive with detection of < 0.1% proportion of clonal cells.

Dense, striated, lymphohistiocytic infiltrate, cell polymorphism, epidermal and vascular involvement. Pleomorphies, hyperchromasia or mitoses may be signs of malignancy, but rarely occur.

Transition to malignant lymphoma.

Favourable (monitoring of clinical course and ensuring absence of metastasis).

1. Braun RP et al. (2000) Cutaneous pseudolymphoma, lymphomatoid contact dermatitis type, as an unusual cause of symmetrical upper eyelid nodules. Br J Dermatol 143: 411-414
2. Böer A et al. (2008) Pseudoclonality in cutaneous pseudolymphomas: a pitfall in interpretation of rearragnement studies. Br J Dermatol 159: 394-402
3. Cogrel O et al. (2001) Sodium valproate-induced cutaneous pseudolymphoma followed by recurrence with carbamazepine. Br J Dermatol 144: 1235-1238
4. Gerlini G et al. (2003) Specific immune therapy-related cutaneous B-cell pseudolymphoma with following dissemination. J Eur Acad Dermatol Venereol 17: 208-212
5. Kulow BF et al. (2002) Progression of cutaneous B-cell pseudolymphoma to cutaneous B-cell lymphoma. J Cutan Med Surg 6: 519-528
6. Moreno-Ramirez D et al. (2003) Cutaneous pseudolymphoma in association with molluscum contagiosum in an elderly patient. J Cutan Pathol 30: 473-475
7. P. Altmeyer Enzyklopädie der Dermatologie, Venerologie, Allergologie und Umweltmedizin, 2. Auflage