Cutaneous pseudolymphomas: inflammatory reactive proliferations

Abstract

Skin is an organ of the immune and lymphoid systems. Lymphoid tissue analogous to gut mucosa-associated lymphoid tissue proliferates in the skin in response to antigenic stimulation. This putative skin-associated tissue is called skin-associated lymphoid tissues (SALT). In the opinion of this author, cutaneous pseudolymphomas represent inflammatory, reactive proliferations of SALT following antigenic stimulation of the cutaneous immune cells. Cutaneous pseudolymphomas commonly involve the exposed areas such as head and neck region and upper extremities. They appear as localized nodules, plaques or noduloplaques. They include B- and T-cell pseudolymphomas. Their histologic patterns include nodular, diffuse, band-like and folliculitis-like morphology. Most pseudolymphomas are idiopathic, but some are secondary to known etiologies (drug intake, arthropod assaults, infectious agents and traumas). Cutaneous pseudolymphomas are usually polyclonal proliferations that regress spontaneously or after treating the underlying etiology. Rare cases harbor clonal lymphoid populations and can progress to low-grade lymphomas. Herein, the author reviews the etiology, clinicopathologic features and diagnosis of the cutaneous pseudolymphomas.

Keywords::

• inflammatory conditions
• pseudolymphomas
• skin

Financial & competing interests disclosure

The author has no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

No writing assistance was utilized in the production of this manuscript.

Key issues

• • Cutaneous pseudolymphomas are inflammatory conditions that result from reactive proliferation of skin-associated lymphoid tissues. They represent ‘exuberant lymphoid tissues’ that have immunoarchitectural features analogous to those of ‘reactive lymph nodes’.

• • The head and neck region and extremities are the most common sites of cutaneous pseudolymphomas.

• • Cutaneous pseudolymphomas have a wide range of clinical presentations and histological features that may be misinterpreted clinically or histologically or both as cutaneous lymphomas. Misinterpretation of pseudolymphomas as lymphomas may result in unnecessary and hazardous treatment.

• • The presence of ‘top-heavy’ dermal infiltrates is not a reliable criterion for separating pseudolymphomas from lymphomas. A ‘top-heavy’ infiltrate may be seen in cutaneous B-cell lymphomas. Moreover, in pseudolymphomas, there may be deep dermal ‘bottom-heavy’ lymphoid infiltrates.

• • The immunophenotypical features and molecular analysis (clonality) may help separate cutaneous pseudolymphomas from lymphomas. Correlation with clinical, immunomorphologic and molecular features as well as follow-up data help in the differential diagnosis between cutaneous lymphoma and pseudolymphomas.