An assessment tool for dactylitis

Philip Helliwell

Definition of dactylitis

Uniform swelling of a digit such that the soft tissues between the joints are diffusely swollen to the extent that the actual joint swelling can no longer be independently recognised.

Adapted from: Rothschild BM, Pingitore C, and Eaton M. Dactylitis: implications for clinical practice. Seminars in Arthritis & Rheumatism. 1998;28:41-7

Dactylitis instrument based on a surrogate of volume

• Joint circumference measurement has a long history in rheumatology (but poor inter-rater reliability)

• Use contralateral digit as comparator

• Easily measured in both finger and toes

• Provides a definition for borderline cases eg 10% difference in circumference

Final instrument

• Based on finger and toe circumference

• Incorporates a score for tenderness based on Ritchie method– 0 = no tenderness on squeezing– 1 = tender– 2 = tender and wince– 3 = tender and withdraw

What if opposite digits are involved?

• Normative data for fingers are available from an anthropometric survey of British workers in the 1980s

• Normative data for toes required – data on 50 people (1,000 digits) collected for this study

Case 1:

1 dactylitic finger

Score 28.4

Injected with steroid

1 week later score 4.6

Case 2:

4 dactylitic digits

Both 2nd toes involved

Total score 96.1

Dactylitis – can we agree?

Previous work Dafna Gladman has shown moderate inter-observer agreement:Kappa statistic 0.57

Reliability study

• 7 patients all with psoriatic arthritis • 5 health professionals (4 physicians and 1

specialist nurse)• No pre-study training given• Assessed patients in turn scoring:

– Presence or absence of dactylitis and tenderness score

– Measured circumference of all 20 digits

• Repeated above after interval of 60 minutes

Circumferometer

Patient 4 in reliability study

Patient 1 in reliability study

Reliability – agreement statistics

• Percentage exact agreement by joint

• Kappa statistics for– tender and non-tender dactylitis– Between and within observers

Percentage exact agreement by digit

0102030405060708090

100

perc

enta

ge

thum

bin

dex

mid

dle

ring

little

gr to

e2n

d toe

mid

dle to

e4t

h toe

little

toe

Median agreement 93%

Inter observer agreement – first examination

Inter observer agreement for presence of tender dactylitis. Kappa statistics are based on recorded tender dactylitis for 140 digits.

00.10.20.30.40.50.60.70.80.9

A B C D

B

D

B

C

D

E

Tender dactylitis

Overall kappa 0.54

Inter observer agreement – first examination

Inter observer agreement for presence of non-tender dactylitis. Kappa statistics are based on recorded tender dactylitis for 140 digits.

0

10

20

30

40

50

60

70

A B C D

B

D

B

C

D

E

Non-tender dactylitis

Overall kappa 0.17

Kappa agreement statistics intra-rater

• Any tender dactylitis: 0.82

• Any non-tender dactylitis: 0.58

Dactylitis instrument

• Median and inter-quartile range

• Intra-class correlation coefficients

Raw dactylitis scores by patient

10101010101010N =

PATIENT

8765421

SC

OR

E1

500

400

300

200

100

0

-100

RDM

PSH

RDM

ICC statistics

1. Inter-rater 0.90, 95% CI 0.74 – 0.98

2. Intra-rater 0.84, 95% CI 0.71 – 0.92

Revised instrument

Variation may exist as a result of:– Differences in measuring circumference– Differences in judging degree of swelling– Differences in assessing response to squeeze

Difference in digital circumference for tender dactylitis by examiner

1313131314N =

EXAMINER

ISJFGIRDMPSH

perc

ent

age

diff

eren

ce

- al

l ten

der

dac

tylit

is70

60

50

40

30

20

10

0

-10

59

54

46

66

Median = 11.7%

Revised instrument

• Variation may exist as a result of:– Differences in measuring circumference– Differences in judging degree of swelling– Differences in assessing response to squeeze

Revised instrument records presence or absence of tenderness and uses 10% cutoff to define dactylitis

Revised dactylitis instrument scores

10101010101010N =

PATIENT

8765421

AL

TER

NA

TIV

E S

CO

RE

300

200

100

0

-100

B

B

B

B

B

ICC statistics

1. Inter-rater 0.76 (0.48 – 0.94)

2. Intra-rater 0.91 (0.83 – 0.95)

ICC statistics

1. Inter-rater 0.76 (0.48 – 0.94)

2. Intra-rater 0.91 (0.83 – 0.95)

1. Inter-rater 0.97 (0.90 – 0.99)

2. Intra-rater 0.91 (0.83 – 0.95)

Dactylitis instrument - revised

Limits of agreement (mean difference ± 2xsd):

All raters: - 5.4 ± 37.4 (-2 ± 17)

Individual raters:

MEAN LOA

PSH -1.3 6.8

RDM -19.3 70.4

GI -3.3 35.4

JF 1.6 8.4

IS -4.8 17.2

Dactylitis assessment tool

Quick and easy to measure

Intra- and inter-rater reliability:

good by ICC

individually variable by LOA

Still require data on responsiveness in a clinical trial setting