Once in a lifetime: Mycosis fungoides
Continuing our series on conditions GPs may only encounter once in their career, GP dermatology specialist Dr Anna Trigell explains how not to miss a case of mycosis fungoides
What is it?
Contrary to the name, it is not anything to do with a fungal infection. The alternative term primary cutaneous T-cell lymphoma is more self-explanatory, but encompasses both mycosis fungoides and Sezary syndrome – a rarer, more aggressive variant.
Mycosis fungoides is a cancer of CD4+ lymphocytes that primarily involves the skin. It tends to run an indolent course passing through several distinct stages, each of which can last many years.
It is a cutaneous form of non-Hodgkins lymphoma. However, while internal non-Hodgkins lymphoma can spread to the skin, this is not classified as mycosis fungoides.
No causes have been identified but people who are immunosuppressed are at increased risk.
How rare is it?
The UK incidence of mycosis fungoides is around 1 per 100,000 people annually. This means a GP with an average list size of around 2,000 may only come across one case themselves in a lifetime of practice. Due to historical difficulty and delay with diagnosis, the true incidence may be slightly higher, however.
Clues for early detection
The condition tends to start around 50-70 years of age and is more common in men with a 2:1 ratio. Younger age of onset can occur in people with Black and Asian ancestry. A high index of suspicion is required, as it can look very different across individuals and with variations in skin tone.
Consider this condition when irregularly shaped, finely scaled or smooth, poorly defined red areas appear on the skin, usually on areas not exposed to the sun, often mimicking eczema or psoriasis. These patches are commonly found around the buttocks, thighs, upper arms and torso (patch stage; see image 1). They can be atrophic (thin and wrinkled) and may appear hypo or hyper pigmented in skin of colour. Dermoscopy of the patches may show fine short linear vessels with spermatozoan vascular structures (very specific for this condition), white scale and a yellow/orange colour. It is itchy in 80% of cases which can sometimes be generalised, and itch can precede the rash.
Image 1. Mycosis fungoides (patch stage) lesions on back of 32-year-old female
A key clue is the lack of sustained response to conventional treatments such as steroid creams and emollients. These may help symptoms and patches can partially improve but never fully resolve.
The patches can slowly, over years, turn into plaques (plaque stage). These plaques are usually well demarcated and can be thickened and are classically annular or arciform due to central clearing and can be red, purplish or brown (see images 2 and 3).
Image 2. Mycosis fungoides (plaque stage) lesions on abdomen of 65-year-old female
Image 3. Mycosis fungoides (plaque stage) lesions on back of 50-year-old male
The plaques can eventually develop into large deep lumps in the skin that may ulcerate (tumour stage, see image 4). Tumours tend to be large and irregular nodules arising from plaques and can be deep red to purplish in colour, often with a shiny surface.
Image 4. Mycosis fungoides (tumour stage) lesions on back of 76-year-old male
May be confused with…
Almost anything – for example, eczema, psoriasis (especially in the plaque stage), fungal infections (particularly if hypopigmented or ring like), pityriasis rosea, intertrigo or any other inflammatory dermatosis. Tumours can mimic other skin malignancies.
Even skin biopsies may not be diagnostic and several may be required before the diagnosis is made. Blood tests are usually normal.
Red flags
- Persistent rash in sun-protected areas associated with long-term itch, occasionally pain.
- Failure to respond as expected to conventional treatments for more common skin conditions.
- Rash gradually evolving into infiltrated plaques over time.
Usual treatment and prognosis
The condition is very slowly progressive and diagnosis is often delayed by several years due to its resemblance to more benign conditions. On average it takes around three to four years to get a confirmed diagnosis.
Despite this, the prognosis for the early stages is generally good with most people having a normal life expectancy due to the slow progression, with long periods of remission. Only around 10% progress to the more advanced life-limiting stages.
Treatment is divided into several options depending on the staging.
In the early stages, a watch and wait approach with skin-directed symptom control is often enough. This may be a combination of emollients, topical steroids, topical retinoids, phototherapy or possibly radiotherapy. This may allow the condition to be manageable as a chronic skin condition in the majority of patients.
In more advanced stages, more aggressive treatments may be required including immunotherapies, monoclonal antibodies, chemotherapy, extracorporeal photopheresis (treating blood with UV light), oral steroids and haematopoietic stem cell transplant from healthy donors.
In summary, although rare, consider mycosis fungoides in anyone of middle age onwards, with a centrally distributed, often itchy, treatment-resistant rash around the torso and limb girdles which seems to gradually evolve despite periods of respite with topical treatments and which doesn’t quite fit with the expected clinical picture of more common inflammatory skin conditions.
Dr Anna Trigell is a GPwER in dermatology at Buckden Community Dermatology Service and a prison GP at HMP Littlehey
Sources and further information
- dermnetnz.org: Mycosis fungoides
- Primary Care Dermatology Society. Clinical guidance: Lymphoma and leukaemia cutaneous presentations
- British Association of Dermatologists. Patient information leaflets. Mycosis fungoides
- Cutaneous Lymphoma Foundation: Mycosis fungoides
- Lymphoma action: Skin (cutaneous) T-cell lymphoma
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