The most typical example of this group of lymphomatoid infiltrates is nodular scabies but many other arthropods can induce skin lesions that may simulate malignant lymphoma histopathologically. Clinically, in nodular scabies, elevated round or oval bright reddish papules and nodules occur most frequently on the genitalia, elbows and in the axillae (Fig. 20.34). The lesions are found in approximately 7% of patients with scabies. The nodules are very pruritic and may persist for many months.
The mite and its parts are seldom identified in the longstanding papules or nodules of scabies. The clinical differential diagnosis includes prurigo nodularis and malignant lymphoma; some lesions of secondary syphilis may be diagnosed incorrectly as a pseudolymphoma of this type.
Histologically, dense superficial and deep perivascular predominantly lymphohistiocytic infiltrates with plasma cells and varying numbers of eosinophils are seen (Figs 20.35 & 20.36) . Eosinophils are also scattered among collagen bundles. Prominent vessels with thickened walls lined by plump endothelial cells are nearly always found. The epidermis may be slightly spongiotic, hyperplastic and hyper-keratotic. Large atypical lymphocytes can be observed. The histological features of nodular scabies may mimic those of mycosis fungoides, lymphomatoid papulosis or Hodgkin lymphoma. Occasionally, a B-cell pattern analogous to lymphocytoma cutis can be recognized in persistent nodular arthropod bite reactions.
Immunohistological investigations reveal that T lymphocytes predominate in nodular scabies. Although previous reports claimed that the use of antibodies for CD30 differentiated the skin lesions of persistent arthropod bites from those of lymphomatoid papulosis because the first are negative, in contrast to the latter that are positive , in truth in some cases of scabies the CD30 antigen can be seen in the large lymphoid cells.
Antiscabietic therapy is usually ineffective in cases caused by Sarcoptes scabiei. Large nodules may be excised surgically. Intralesional injection of corticosteroids may be helpful. Spontaneous resolution in time is the rule.
Was this article helpful?