Should you use your hand to measure skin involvement or calculate amount of topical agents?

What percentage of total body surface area is involved? The answer to this question is necessary in computing severity scores, such as the Psoriasis Area Severity Index (PASI), the Atopic Dermatitis Severity Index (ADSI), the SCORing Atopic Dermatitis Index (SCORAD), and the mSWAT (Modified Severity Weighted Assessment Tool) for measuring cutaneous T-cell lymphoma.

Traditionally, calculations of percentage of body surface involvement are made by (1) the palmar method (surface area of the palm including fingers and thumb is considered roughly equal to 1% of body surface area); (2) the Rule of Nines (the body is divided into areas considered to equal 9%, or a multiple of 9%, of the total area; see figure); or (3) estimation from a Lund and Browder chart. The palmar method is best for small calculations of disease in small body areas, but it can be incorrect for larger areas, because the area of the palm including fingers and thumb depends on sex, weight, age, and other factors.

The authors discuss various systems of measurement and published studies related to calculation of body area. They conclude that a modified palmar method is the most convenient reliable measure for small disease areas. In the modified version, the area of the palm not including the fingers and thumb is assumed to constitute 0.5% of total body area. The authors have developed an iPhone app that is especially useful for mSWAT scoring of cutaneous T-cell lymphomas.

CITATION(S):

Scarisbrick JJ and Morris S. How big is your hand and should you use it to skin score? Br J Dermatol 2013 Apr 29; [e-pub ahead of print].