What is cutaneous pseudolymphoma?
Cutaneous pseudolymphoma refers to a group of conditions that simulate a lymphoma (blood cell cancer), but behave in a harmless manner. In most situations this appears to be a reactive process, though a number of dermatologic conditions can be difficult to distinguish from a lymphoma.
Classification of cutaneous pseudolymphomas 
- Actinic reticuloid
- Lymphomatoid contact dermatitis
- Lymphomatoid drug reaction, T cell type
- Solitary T-cell pseudolymphoma (‘unilesional mycosis fungoides’)
- Lichenoid (‘lymphomatoid’) keratosis
- Lichenoid pigmented purpuric dermatitis
Conditions that can simulate lymphomatoid papulosis / anaplastic large cell lymphoma, and are CD30+ include:
- Orf – Milkers nodule
- Herpes simplex and
- Molluscum contagiosum
- Arthropod (insect) reactions (including nodular scabies).
Lupus panniculitis can simulate subcutaneous T-cell lymphoma
Conditions that simulate B cell lymphomas (follicle center lymphoma, marginal zone B-cell lymphoma, large B-cell lymphoma) include:
- Lymphocytoma cutis
- Lymphomatoid drug reaction, B cell type
- Pseudolymphoma after vaccination
- Pseudolymphoma in tattoos
- Pseudolymphoma caused by Hirudo medicinalis therapy
Jessner's lymphocytic infiltrate can simulate chronic lymphocytic leukaemia, B cell type.
Inflammatory pseudotumour can simulate plasmacytoma and marginal zone B-cell lymphoma.
Clinical features and diagnosis of pseudolymphoma
The original description applied only to lymphocytoma cutis. Over time a number of other conditions have been added to this category, as reports of conditions mimicking a lymphoma have been described. This is largely based on the histological (microscopic) appearance.
The presentation and behaviour depends on which the particular subtype. Most cases tend to resolve spontaneously if the precipitating agent is removed. Some may recur over time.
The diagnosis of pseudolymphoma is made by both a combination of the clinical features and careful histological analysis. Often the diagnosis can be confirmed only by observing the behaviour of the condition over time.
Treatment of pseudolymphoma
Treatment is dependent on the particular subtype, but in cases resulting from a reactive process, observation may be all that is required.