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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.