Mixed diagnoses – 10 cases (2 of 11)

Psoriasis

Psoriasis results in relatively constant, well-demarcated plaques. It tends to be bilateral and roughly symmetrical, affecting similar sites on the feet. The main complaints are discomfort due to fissuring and the unsightly appearance. Psoriatic nail dystrophy is likely if the psoriasis affects the tips of the digits. Typical psoriatic plaques are frequently present in the scalp, on elbows, knees and/or body folds.
Psoriasis may be confused with other types of inherited or acquired palmoplantar keratoderma. These are characterised by thickened yellowish localised plaques or diffusely thickened skin and the absence of typical psoriasis elsewhere.

There is no specific test for psoriasis in this site. Scrapings for mycology may be appropriate if the diagnosis is uncertain. A solitary lesion might be confused with squamous cell carcinoma in situ, when a biopsy might be helpful.

In general, psoriasis affecting the palms should be protected from frictional injury, lubricated and soothed with emollients. Hand creams should be thick, and a thin amount should be applied frequently to reduce fissuring. They are not permitted in certain jobs (e.g. car painters), when they should be used liberally after hours. No specific protection from chemical irritants or water is required.
As keratinocytes form a thick 'brick wall' in palmar skin, drugs penetrate poorly. Psoriasis can be treated with ultrapotent topical steroids, applied no more than once or twice daily and accurately to the affected area. Typically, a steroid ointment is used for about four weeks, and then pulsed at weekends for four to eight weeks. Continued use of ultrapotent topical steroids should be regularly reviewed, particularly if the patient has psoriasis, because of the risk of tachyphylaxis and skin atrophy. Calcipotriol is occasionally helpful, but inadvertent application might result in an irritant contact dermatitis on the face. Tar or dithranol preparations tend to be too messy to be practical in this site.
Severe and/or persistent psoriasis interfering with function may require specialist consultation and second line treatments. These may include phototherapy, acitretin, methotrexate or ciclosporin.