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Table 1 Characteristics of the different patient groups studied with juvenile idiopathic arthritis and related disorders

From: Early onset pauciarticular arthritis is the major risk factor for naproxen-induced pseudoporphyria in juvenile idiopathic arthritis

Characteristics PP+ (n = 45) PP- (n = 96) CO (n = 55) PP+ versus PP- PP+ versus CO
Female (%) 76 65 58   
Mean age (years) 4.7 8.2 8.6 P < 0.01a P < 0.01a
Laboratory findings      
   Haemoglobin level <11.8 g/dl (%) 61 34 24 P < 0.01b P < 0.01b
   Mean white blood cell count (cells/μl) 10,440 8,000 8,110 P < 0.01a P < 0.01a
   Mean platelet count (×10e3/μl) 409 362 332   P < 0.01a
   ESR >11 mm/hour (%) 71 51 30 P < 0.01c P < 0.01c
   Positivity for ANAs (%) 51 45 24   P < 0.05b
Factors relating to the skin      
   SPT I and II (%) 58 39 53 P < 0.05b  
   Freckles (%) 42 34 36   
   Blue/grey eye colour (%) 68 72 60   
   Fair hair colour (%) 61 50 51   
   Regular skin care (%) 82 75 82   
   Intense sun exposure during vacation (%) 47 31 25   P < 0.05b
   Photoprotective measures (%) 89 83 85   
   Application of sun screen with >20 SPF (%) 44 50 42   
   Atopic diathesis (%) 21 25 16   
   Psoriasis (%) 8 3 2   
Factors relating to naproxen therapy and comedication      
   Mean duration of naproxen therapy (months) 22.8 20.2 -   
   Mean dosage of naproxen (mg/kg per day) 16.7 15.5 -   
   Maximal mean dosage of naproxen (mg/kg per day) 17.6 16.7 -   
   Increased naproxen dosage during the course of treatment (%) 42 24 - P < 0.05b  
   Comedication (%) 58 38 - P < 0.05b  
   Chloroquine as comedication (%) 27 6 - P < 0.01b  
  1. aMann-Whitney U-test. bχ2 test. ct-test for independent samples. ANA, antinuclear antibody; CO, children not treated with naproxen (controls); ESR, erythrocyte sedimentation rate; PP+, children treated with naproxen who developed pseudoporphyria; PP-, children treated with naproxen who did not develop pseudoporphyria; SPF, sun protection factor; SPT, skin phototype.