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Rheumatology 2008 47(2):219-221; doi:10.1093/rheumatology/kem353
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© The Author 2008. Published by Oxford University Press on behalf of the British Society for Rheumatology. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Sparing of the thumb in Raynaud's phenomenon

B. Chikura1, T. L. Moore2, J. B. Manning2, A. Vail3 and A. L. Herrick2

1The Royal Liverpool University Hospital, Liverpool, 2Rheumatic Diseases Centre and 3Biostatistics Group, University of Manchester, Hope Hospital, Salford, UK.

Correspondence to: B. Chikura, The Royal Liverpool University Hospital, Prescot Street, Liverpool L7 8XP, UK. E-mail: docbatsi{at}aol.com


   Abstract
Top
 Abstract
Introduction
 Patients and methods
 Results
 Discussion
 References
 
Objectives. To conduct a prospective study to determine which digits are affected (and whether the thumb is spared or not) in a cohort of patients with RP as assessed by symptoms and thermography and to determine whether the degree of thumb involvement differs between primary (PRP) and secondary Raynaud's phenomenon (SRP).

Methods. This was a cross-sectional study of 44 patients with RP. The following characteristics were recorded to allow comparisons between digits: symptoms of RP in each digit (graded on a scale of ‘never’, ‘sometimes’ and ‘always’ affected during an attack of RP) and thermography at 23°C. A distal–dorsal difference (DDD) in temperature at 23°C of –1°C or less was considered to be clinically relevant.

Results. Symptom scores in the thumb were significantly better, i.e. less severe than in each finger (P < 0.001). As only three participants had any finger better than the thumb, there was no power to compare whether the thumb was spared more in PRP compared with SRP. Mean DDD was significantly higher (i.e. better) in the thumb compared with each finger (P < 0.001). Although DDD scores were higher in PRP compared with SRP (P = 0.01), there was no evidence that the relative effect of the thumb differed between the two groups (P = 0.26).

Conclusions. Our findings confirm that the thumbs are spared in RP, both primary and secondary, as demonstrated by both symptoms and thermography. The reasons for sparing of the thumb were not addressed in this study but raised questions regarding pathophysiolgy.

KEY WORDS: Raynaud's phenomenon, Thumb, Thermography, Systemic sclerosis


   Introduction
Top
 Abstract
 Introduction
Patients and methods
 Results
 Discussion
 References
 
In RP, classically the digits turn white (vasospasm), then blue (deoxygenation of static venous blood), then red (reperfusion) in response to precipitating factors such as cold exposure or emotional stress [1, 2]. RP can be divided into primary and secondary depending on absence or presence of an underlying disease/disorder, respectively. For example, connective tissue diseases (CTDs) such as SSc [3].

There are many methods that have been developed over the years to quantify digital vascular involvement in RP. These include nailfold capillaroscopy, laser Doppler flowmetry, thermography and finger systolic blood pressure [4, 5]. It has been observed using these techniques that digital involvement is not uniform and anecdotally, many patients when specifically asked report that the thumb is spared. Yet, to our knowledge there are no previous studies that have looked into thumb involvement. If the thumb is not involved, this raises the question as to why this is the case. The other question is whether thumb involvement is of prognostic value, i.e. do those patients who have RP affecting thumbs have more severe disease than those without? The difference in the degree of thumb involvement between primary Raynaud's phenomenon (PRP) and secondary Raynaud's phenomenon (SRP) has not been previously investigated. This could be clinically important and might assist in clinical classification. If there is a difference in thumb involvement between PRP and SRP this could imply different pathophysiologies.


   Patients and methods
Top
 Abstract
 Introduction
 Patients and methods
Results
 Discussion
 References
 
Patients
Forty-four patients (6 males, 38 females) were recruited at Hope Hospital between November 2006 and April 2007. The median age was 46 yrs and the range was 18–71 yrs. The median duration of symptoms was 47 months, range 2–540 months. Only patients with definite RP (defined by at least two colour changes, one of them being white in response to cold or emotion), 18 yrs or older and able to give consent were recruited.

Fourteen patients (2 males, 12 females) fulfilled the LeRoy and Medsger [6] criteria for PRP. Thirty patients (4 males, 26 females) were classified as SRP [6, 7]. Twelve patients had SSc, 10 patients had the limited cutaneous and two had the diffuse cutaneous subtype [8]. Thirteen patients had undifferentiated CTD (UCTD) (2 males, 11 females). These patients had features that precluded the diagnosis of PRP but did not have a specific CTD. All patients with UCTD were antinuclear antibody (ANA)-positive (positivity was defined by an IgG titre of >1/100). Nailfold capillaroscopy was done in 9 of these 13 patients and three had abnormal findings. One patient had mixed CTD (MCTD) and was positive for UI-RNP antibody, three patients (all female) had primary Sjögren's syndrome (one patient was positive for anti-Ro/La antibodies) and one patient had cold agglutinin disease.

Twelve patients (27%) were on vasoactive drugs such as calcium channel blockers and angiotensin-converting enzyme inhibitors. Of the 12 patients who were on vasoactive drugs, 10 patients (83%) fulfilled the criteria for SRP, and two patients (17%) the criteria for PRP. Twenty-four patients (55%) had a history of smoking and 13 patients (30%) were current smokers.

Methods
Symptoms
The following information was recorded by patients to assess the frequency and severity of symptoms of RP:

  1. Colour changes in digits during an attack of RP (options of white, blue and red were given to patients and they could select one or more of the three colour changes) as noted by the patient.
  2. The frequency of symptoms was graded on a scale of ‘never’, ‘sometimes’ and ‘always’ involved for each digit as noted by the patient.
  3. The ‘worse’ of the left and right scores for each digit (‘never’ being the best of the three scores, ‘always’ being the worst and ‘sometimes’ in between) were considered for analysis. For example, if the left thumb score was ‘sometimes’ and the right thumb was ‘never’, ‘sometimes’ involved was considered for analysis.

The study was approved by the Warrington, Wigan and Leigh Research Ethics Committee and all subjects gave informed consent.

Thermography
The camera used was an Agema 570 infrared thermography camera (Flir Systems Limited) with the Agema Research 2.1 programme software installed on a standard desktop computer. Thermography was performed by a senior vascular technician using a standard thermography protocol used at Hope Hospital. Patients were asked to refrain from caffeine/nicotine for 4 h prior to testing. After acclimatization at 23°C for 20 min in a temperature-controlled room an image of the dorsum of each hand was taken, and from these hand images the distal–dorsal difference (DDD) was calculated, i.e. the temperature of the tip of the fingers minus the temperature of the dorsum of the hand. A DDD of –1°C or less at 23°C was considered to be clinically relevant involvement [9, 10]. The worst score (the lower score, i.e. the more negative value) from each pair of digits was considered for analysis. Results of DDD at 23°C were compared between the fingers and the thumbs to assess the degree of thumb involvement and to compare between PRP and SRP.

Sample size
It was calculated that 16 patients per group (i.e. PRP and SRP) would allow detection of a difference of 1 S.D. in the outcome (e.g. the average temperature gradient along the thumbs) with 80% power. However, it was considered that the ratio between PRP and SRP would be 1:3, requiring 11 patients with PRP and 33 with SRP.

Statistical analysis
The results were analysed using McNemar's test and repeated measures analyses of variance (ANOVA).


   Results
Top
 Abstract
 Introduction
 Patients and methods
 Results
Discussion
 References
 
Symptoms
Comparison of symptom frequencies on a scale of ‘always’, ‘sometimes’ and ‘never’ did not show that digits were different with the exception of the thumb, which was less frequently involved (P < 0.001) (Table 1). Eighteen patients (41%) had never had their thumbs affected by RP as compared with none for the middle finger, i.e. all patients reported middle finger involvement. Four patients (9%) indicated that their thumbs were always involved, and in comparison 31 patients (70%) reported that their middle fingers were always involved. As only three participants had any finger better than the thumb, there was no power to compare PRP and SRP.


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  		TABLE 1. Comparison of frequency of symptoms between thumbs and other digits

 
Thermography
Proportions of different digits with a DDD of –1°C or less
The proportions of thumbs with clinically relevant DDD, i.e. a DDD of –1°C or less, showed that the thumb was the least affected digit; 18% of thumbs compared with 64% in the index finger had clinically relevant DDD (Table 2).


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  		TABLE 2. DDD in the different digits showing (i) numbers of digits with a clinically relevant temperature gradient, i.e. DDD of –1°C or less and (ii) the mean DDD for each digit for the whole patient cohort and for the subgroups with PRP and SRP.

 
Absolute temperature gradients of digits
The thumbs were warmer compared with other digits (Table 2). The mean DDD for the thumbs was significantly higher, i.e. warmer, compared with other digits (P < 0.001). Patients with PRP had higher values than those with SRP (P = 0.01, ANOVA) (Table 2). Although there were greater differences between thumb and other finger DDD scores in SRP compared with PRP, these were not statistically significant (P = 0.26) and this could be due to low power to detect the interaction.


   Discussion
Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
References
 
This is the first study to look specifically at thumb sparing in RP. Our findings show that the thumb is spared as reported by patients. Symptoms were comparable in all digits with the exception of the thumb, which was significantly less frequently involved. This was confirmed by thermography. The mean DDD of the thumbs was higher (i.e. their tips were warmer) compared with other digits, and the proportion of thumbs with a DDD of –1°C or less at 23°C was lower than that for the other digits.

The degree of thumb sparing was more pronounced in the SRP group compared with PRP group (Table 2). Although DDD scores were higher (better) in PRP compared with SRP, there was no evidence that the relative effect of the thumb differed between the PRP and SRP. If the thumb is more involved in SRP as compared with PRP, this observation raises the question as to whether thumb involvement is of prognostic value, i.e. do those patients who have RP affecting the thumb have more severe disease than those without? The question as to whether thumb involvement differs between PRP and SRP is clinically relevant to a rheumatologist in that this may help distinguish the two conditions and imply different pathophysiologies. Vascular problems in PRP are mainly functional; in contrast, structural vascular abnormalities can be seen in patients with SRP, demonstrated by nailfold capillaroscopy. Larger studies are required to compare thumb involvement between PRP and SRP.

In this study, we have used both subjective (self-reporting of symptoms of RP) by patients and objective (thermography) methods to assess the degree of thumb involvement. Thermography is a non-invasive technique that has been applied in assessing the degree of digital vascular response to cold [11, 12]. Thermography can help to distinguish between normal, PRP and SRP [13, 14] and relies on measuring the skin temperature as an indirect measure of digital blood flow. The DDD in temperature measures the temperature difference between the fingertips and dorsum of fingers, i.e. the temperature of finger tips minus the temperature dorsum of the hands. The value obtained is usually negative in patients with RP because the dorsum of the hand is warmer than the tips of fingers. A DDD of less than –1°C (dorsum warmer than the tip of fingers) at 23°C can distinguish between healthy subjects and patients with RP [10]. A DDD of –1°C or less was therefore used in this study for clinically relevant involvement. Thermography has a good positive predictive value and negative predictive value, in patients with RP, for hand–arm vibration syndrome [15, 16] and SSc [9].

This study has generated more questions than answers. We have demonstrated that the thumb is spared in RP but this raises the question as to why this is the case. A search for the answer could lead us to a greater understanding of the pathophysiology of RP. The anatomical differences between the thumb and other digits could help explain thumb sparing. It is the shortest and ‘fattest’ digit and important for movements that require precision and a power grip. It is the only digit with two instead of three phalanges. The blood supply to the thumb differs from that of other digits. The dorsal arterial blood supply to the thumb is well developed and is represented by an independent vascular axis, in contrast to other digits in which the dorsal arteries are inconsistent and dependent on the palmar circulation [17]. The thumb may be protected from adverse vascular events such as RP by a rich blood supply. The length of the digits (and their arteries) could be crucial in determining the clinical expression of RP. There is some evidence in this study to support this hypothesis. The thumb is the shortest digit and is the least involved. The little finger, which is the second shortest finger, appears to be the second least affected finger after the thumb, whereas the middle finger, which is the longest digit, is the worst affected digit as assessed by the frequency of self-reported symptoms of RP (Table 1). The critical distance could be the distance between the palmar and dorsal vascular arches and the tip of the finger as this represents the length of digital arteries. However, explaining thumb sparing in RP based solely on anatomical differences may be simplistic.

Our cohort is representative of patients referred to a rheumatology clinic with RP. Fewer than half of the patients attending routine rheumatology clinics with RP have a specific CTD [18]. In our cohort, 16 patients (36%) had a specific CTD. In secondary care, most RP patients have SRP; however, this includes patients who have characteristics that preclude the diagnosis of PRP but have no identifiable CTD. This is in contrast to general practice in which there are more patients with PRP (80%) compared with SRP (20%) [19].

In conclusion, our findings confirm that the thumbs are spared in RP, both primary and secondary, as demonstrated by both symptoms and thermography. The reasons for sparing of the thumb were not addressed in this study but raise questions regarding pathophysiology. Thumb involvement may have prognostic value, pointing to an underlying CTD and/or increased severity of RP. This hypothesis should be tested in prospective studies.

Formula

Disclosure statement: The authors have declared no conflicts of interest.


   References
Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 

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Submitted 21 September 2007; revised version accepted 30 November 2007.
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B. Chikura, T. Moore, J. Manning, A. Vail, and A. L. Herrick
Comment on: Sparing of the thumb in Raynaud's phenomenon: reply
Rheumatology, August 1, 2008; 47(8): 1260 - 1260.
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Comment on: Sparing of the thumb in Raynaud's phenomenon
Rheumatology, August 1, 2008; 47(8): 1260 - 1260.
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