Question:

A 59-year old business man complained of a localized persistent itchy rash affecting his lower back for the past four years. The patches were persistent and never disappeared. The itch was constant with some temporary relief with topical application of steroid cream. Skin scrapings from the lesions for microscopic and mycology studies were all negative. His past health was good. Apart from the creams for relieving of pruritus, he had not used other topical preparations over the affected areas. On examination, there was no abnormality of touch or pain sensation in the patches.

Answer: C. Cutaneous T cell lymphoma

A more popular term is Mycosis fungoides. Mycosis fungoides is a low grade T-cell lymphoma and is the commonest variant of primary cutaneous T cell lymphoma. Histologically, there is a polymorphous cellular infiltrate with polymorphonuclear leukocytes, eosinophils, lymphocytes and atypical mononuclear cells. These atypical mononuclear cells have a cerebriform nucleus and are seen within the epidermis either singly or in small clusters forming Pautrier's microabscess and they are primarily helper T cells.

Typically mycosis fungoides is difficult to diagnose in the early phase even with repeated skin biopsy because it is not frequently diagnostic. It begins with persistent pruritic scaly erythematous patches on the trunk that respond poorly to topical therapy. Mycosis fungoides is often found in the skin over the breast, buttock and lower back. The average time from onset of skin lesions to diagnosis is seven years. In early patch stage, a high index of clinical suspicion will alert the pathologists to give an earlier definite diagnosis. It is an indolent and slow progressing disease that may take 10 or more years to develop to plaque and then tumour stage. The erythrodermic mycosis fungoides or Sezary syndrome is less common. Sezary syndrome is the presence of the triad of erythroderma, lymphadenopathy and a population of 10% or more of atypical mononuclear cells in the peripheral blood. The clinical course of this type is closer to T-cell leukaemia than to the true mycosis fungoides. It rapidly runs a downhill course with poor prognosis. The treatment for early stage of mycosis fungoides will be topical steroid and photochemotherapy (PUVA). Actually, this patient is currently under PUVA treatment and there is generalized tanning in the treatment area. Later stages will require systemic chemotherapy and electron beam therapy.

Primary cutaneous B cell lymphoma is rare. Most B cell lymphomas of the skin will present as nodules or tumours from the beginning. Radiotherapy is the preferred mode of treatment for these rare lymphomas. All require histopathological proof and to exclude its being not part of the cutaneous deposits from other systemic leukemoid-lymphoid malignancies.

Leprosy is also known as Hansen's disease in recognition of a Norwegian physician who discovered Mycobacterium leprae in 1873. Leprosy should always be excluded in a persistent cutaneous patch in the lower back or trunk. A persistent skin rash with areas of cutaneous anesthesia e.g. loss of sweating, touch, temperature and pain sensation are the most useful clinical feature for diagnosis of leprosy. Tinea corporis may sometimes be persistent especially after having been mistreated with topical steroid leading to tinea incognito. Skin scrapings for mycology studies will easily detect abundant fungal elements and growth in this category.