Figure 1: Comparison of the PASI and the SPASI in three sample patients
To illustrate the similarity of the PASI and the SPASI, three examples are shown in the tables below. An explanation of the calculations is given with patient 1. Scores for redness, thickness and scaliness, as well as percent area of involvement, were arbitrarily assigned in all three patients. The final column in each table demonstrates the whole body integration of these assigned severity scores and affected area percentages used in the calculation of the SPASI score.
Patient 1
We assume that the redness, thickness and scaliness of all the lesions are all moderate (score of 2 on a 04 scale). We assume 5% of the head is involved, 12% of the upper extremities, 35% of the trunk, and 20% of the lower extremities.
The resulting PASI and SPASI scores would be:

PASI Calculations 
SPASI Calculations 

Head 
Upper extremities 
Trunk 
Lower extremities 
Total body 

1 
Redness 
2 
2 
2 
2 
2 
2 
Thickness 
2 
2 
2 
2 
2 
3 
Scaliness 
2 
2 
2 
2 
2 
4 
Sum of rows 1, 2 and 3 
6 
6 
6 
6 
6 
5 
Affected area (%) 
5 
12 
35 
20 
21.4 
6 
Area score 
1 
2 
3 
2 
2 
7 
Area weights 
0.1 
0.2 
0.3 
0.4 
 
8 
Row 4 * row 6 * row 7 
0.6 
2.4 
5.4 
4.8 
 
9 
PASI (Sum of row 8) 
13.2 
12 
To obtain the SPASI score the clinician would estimate the mean redness, thickness and scaliness of the lesions at 2 each. The total body surface area would be assessed as being between 10 and 30% for an area score of 2 (the actual % total body area involved is [0.1 x 5 + 0.2 x 12 + 0.3 x 35 + 0.4 x 20] or 21.4%). The SPASI = (2 + 2 + 2) x 2 = 12.
Patient 2 (a patient with varying levels of psoriasis severity in all 4 body regions)

PASI Calculations 
SPASI Calculations 

Head 
Upper extremities 
Trunk 
Lower extremities 
Total body 

1 
Redness 
3 
1 
3 
1 
2 
2 
Thickness 
1 
4 
2 
4 
3 
3 
Scaliness 
2 
3 
1 
2 
2 
4 
Sum of rows 1, 2 and 3 
6 
8 
6 
7 
7 
5 
Affected area (%) 
15 
5 
25 
40 
26 
6 
Area score 
2 
1 
2 
3 
2 
7 
Area weights 
0.1 
0.2 
0.3 
0.4 
 
8 
Row 4 * row 6 * row 7 
1.2 
1.6 
3.6 
8.4 
 
9 
PASI 
14.8 
14 
Patient 3 (a patient with involvement in only 2 of the 4 body regions)

PASI Calculations 
SPASI Calculations 

Head 
Upper extremities 
Trunk 
Lower extremities 
Total body 

1 
Redness 
0 
0 
1 
2 
2 
2 
Thickness 
0 
0 
3 
4 
4 
3 
Scaliness 
0 
0 
3 
2 
2 
4 
Sum of rows 1, 2 and 3 
0 
0 
7 
8 
8 
5 
Affected area (%) 
0 
0 
25 
40 
23.5 
6 
Area score 
0 
0 
2 
3 
2 
7 
Area weights 
0.1 
0.2 
0.3 
0.4 
 
8 
Row 4 * row 6 * row 7 
0 
0 
4.2 
9.6 
 
9 
PASI 
13.8 
16 