What is chronic superficial scaly dermatitis?
Chronic superficial scaly dermatitis (CSSD) is a chronic dermatosis that is characterised by round or oval, red, scaly patches primarily on the limbs and trunk.
Also known as chronic superficial dermatitis, parapsoriasis, or digitate dermatosis, CSSD is relatively uncommon and can be subdivided into small (SPP) and large plaque parapsoriasis (LPP). Whilst SPP is thought to be a benign chronic condition, LPP is thought to be potentially premalignant and associated with a risk of progression to mycosis fungoides.
Chronic superficial scaly dermatitis
Who gets chronic superficial scaly dermatitis?
CSSD tends to occur in older individuals, with a male predominance. The exact incidence and prevalence of the condition is unknown.
What causes chronic superficial scaly dermatitis?
The cause of chronic superficial scaly dermatitis is not known.
One hypothesis for its development is that it is a precursor to mycosis fungoides or an early form of the disease. The lesions are mainly comprised of clonal CD4+ T-cells, though the presence of T-cell clones does not appear to increase risk of malignancy.
What are the clinical features of chronic superficial scaly dermatitis?
Chronic superficial scaly dermatitis begins with one or more red, slightly scaly patches mainly on the limbs and trunk.
The patches may be:
- Round or ovoid
- Possess finger-like processes
- Resemble cigarette paper
- Usually asymptomatic but can be mildly pruritic
- Often become more prominent in winter but resolve during summer.
Once the lesions resolve they may recur in the same or adjacent region.
SPP lesions are often 2–5 centimetres in diameter whilst LPP is more than 5 centimetres in diameter. Additionally, LPP may be associated with skin atrophy, telangiectasia, and mottled hyperpigmentation.
CSSD immunostaining also reveals a mature T-cell phenotype made mostly of CD4+ cells with some polymerase chain reaction (PCR) studies showing a dominant clonal pattern of T-cells. The clonal density is noted to be 1–10% but this does not seem to determine propensity to transition to malignancy. Approximately 7.5% to 14% of LPP progress to mycosis fungoides, though most remain benign for many years.
How do clinical features vary in differing types of skin?
Features are similar in all skin types.
What are the complications of chronic superficial scaly dermatitis?
CSSD is a benign condition, though it may resemble cutaneous T-cell lymphoma and have the ability to transform into mycosis fungoides. Hence individuals should be cognisant of changes in skin lesions such as colour, thickening, increase in scaling, crusting, or thinning.
How is chronic superficial scaly dermatitis diagnosed?
The clinical and histological findings consistent with CSSD include:
- Presence of asymptomatic erythematous macules usually on the trunk
- Non-specific histopathological findings consistent with superficial dermatitis
- Persistence of lesions over time and previous resistance to treatment.
A punch biopsy may be taken with histopathological findings of SPP such as:
- Mild acanthosis with parakeratosis
- Superficial perivascular lymphohistiocytic infiltrate
- Plasma collection over basket weave keratin associated with confluent linear parakeratosis is an additional characteristic finding.
LPP is histologically similar to SPP, but can also consist of:
- Epidermal atrophy
- Lymphohistiocytic infiltrates that are lichenoid
- Basal vacuolization with incontinence of melanin.
There may also be atypical or haloed lymphocytes and histological findings may be similar to that seen in mycosis fungoides.
Investigations such as nuclear contour studies, immunohistochemistry, PCR, and T-cell receptor gene rearrangement studies can aid in identifying atypical lymphocytes and hence show which LPP may become mycosis fungoides. However, these methods are not completely accurate. It is thought that earlier genotypic analysis of T-cell receptor rearrangement is the gold standard of all diagnostic tests enabling differentiation between benign and malignant T-cell infiltration.
What is the differential diagnosis for chronic superficial scaly dermatitis?
- Mycosis fungoides
- Pityriasis lichenoides chronica
- Guttate psoriasis
- Pityriasis rosea
- Nummular dermatitis
What is the treatment for chronic superficial scaly dermatitis?
Parapsoriasis does not require treatment but may be treated if symptomatic or if there is cosmetic concern.
- Can be utilised for dryness or scaling
- Topical steroids
- For people who do not respond to topical corticosteroids, phototherapy with broadband or narrowband ultraviolet B (UVB) or, less frequently, psoralen plus ultraviolet A (PUVA) may be suitable
- Can temporarily remove patches
- Phototherapy can be utilised 2–3 times a week for several months until clearance of lesions and subsequently gradually tapered.
How do you prevent chronic superficial scaly dermatitis?
There is no known way of preventing CSSD.
What is the outcome of chronic superficial scaly dermatitis?
The long-term outcome of CSSD is variable. Most cases are present for a person’s lifetime with minor fluctuations, but spontaneous resolution may occur in some individuals.
There are reports of individuals developing mycosis fungoides and hence skin checks every 3–6 months and subsequently yearly with biopsies of suspicious lesions should be conducted. Elevated risk of thromboembolism, acute myocardial infarction, stroke, and cancer including non-Hodgkin lymphoma have been reported with CSSD.