The role of visual signs – are they reliable in peripheral arterial disease (PAD) screening?
1300 Words
9 min. reading time
Sylvia McAra, PHD
Podiatrist, Clinician & Educator
Sylvia has been involved in a number of peer reviewed publications regarding peripheral vascular assessment. Her doctoral project involved using toe-brachial pressure indices to measure outcomes using transdermal glyceryl trinitrate. Now she provides podiatry services at a large multidisciplinary medical practice in Wodonga, Victoria. She is involved in education for evidence-based best practice in peripheral vascular screening.
World Health Day is taking place this month on April 7th with the theme of building a fairer, healthier world. This month’s cardiovascular section is focusing on an aspect of evidence-based practice for peripheral vascular assessment for improved clinical decision-making and preventative care.
In contrast to arterial disease, venous disease is very likely to demonstrate clear early visual signs including oedema, varicose veins, and skin changes in the gaiter area. This highlights the importance of not relying on visual signs, but on valid peripheral arterial screening using appropriate assessments.
There are well known visual signs that are associated with the ischemia of advanced PAD, and these are taught to podiatrists and medicos as part of standard medical education. However, these signs are often mistakenly over-relied on in screening and diagnosis, as they are not present in early disease. The visual signs listed below are in fact, evidence only of peripheral ischemia, a secondary manifestation of late peripheral artery disease. In fact, many people with clinically important PAD are asymptomatic and have no visual signs at all.
Clinical visual examination alone is insufficient to exclude PAD
The presence of pulses does not exclude PAD
Monophasic Doppler is useful to indicate PAD
An ankle-brachial index (ABI) in the normal range does not exclude PAD
Use the ‘WIfI’ classification with toe pressures; recommended for risk evaluation for people with a history of ulceration.
Visual signs indicate peripheral ischemia and only appear in late disease
Visual signs are not valid to screen for clinically important PAD and are not expected in primary PAD (which is the common and widespread vessel disease of atherosclerosis). Atherosclerosis may progress to advanced, life threatening stages before any ischemia of distal tissues occurs. In fact, many people have no visual signs but do have clinically important PAD, which confers risks to their mortality. https://twitter.com/PodiatryToday/status/1380503610451226627See the featured case study for a clinical example.
Asymptomatic and invisible PAD occurs in silent, unappreciated disease and is potentially more dangerous for people, as they are less likely to have their modifiable cardiovascular risk factors addressed.
This is an exciting opportunity for podiatrists to take up to improve health outcomes in screening for vessel disease, which is the etiology behind cardiovascular disease: the greatest cause of mortality in Australia and worldwide. Statistics on this phenomenon are being presented in the next issue of STRIDE.
Occlusive disease is easier to detect than milder atherosclerosis, which is the primary limitation of clinical screening tests for PAD.
The visual signs traditionally associated with the trophic changes of the ischemia associated with severe arterial insufficiency include:
Colour changes: Colour is an important clinical observation with many significant implications, but has been shown to be not specific nor sensitive enough to screen for PAD.
Hair loss: Hair loss is also not reliable as screening for PAD, with false negatives and false positives abounding.
Atrophic skin and nails: These are likely to be associated with reduced tissue perfusion, but also with ageing.
In contrast to arterial disease, venous disease is very likely to demonstrate clear early visual signs including oedema, varicose veins, and skin changes in the gaiter area. This highlights the importance of not relying on visual signs, but on valid peripheral arterial screening using appropriate assessments.
Tests historically over-relied on in peripheral vascular assessment
Pulses: Palpation of foot pulses cannot exclude PAD and should not be the end point of any peripheral vascular assessment. A present pulse indicates only the lack of a complete stenosis. Reliability of pulse palpation declines in the presence of diabetes, neuropathy and oedema. Pulse palpation has low intertester reliability, especially for less experienced clinicians.
Temperature: Temperature is not a sensitive test for PAD screening. Skin temperature measures are influenced by the insulation of clothing, the ambient temperature and the time taken for people to adapt to extrinsic factors when moving from other environments. However, a cooler foot may be a sign of relative ischaemia in critical limb ischemia. Elevated temperatures are important for screening for infection, inflammation and Charcot foot, so temperature testing of both feet should remain an important part of screening. Toe pressures are invalidated when the skin is below 20 degrees, and warming before testing is appropriate if feet are below this threshold, to accurately determine the perfusion potential.
Capillary refill time: This is also called the superficial venous plexus filling time. It is not a valid indicator of arterial supply, being instead, the sum of the opposite pressures between the venous and arterial ends of the peripheral vascular plexus. Interstitial fluid and venous back-pressure provide an unquantifiable pressure gradient opposing the arterial pressure, thus invalidating this test as an indicator of arterial supply.
Occlusive disease is easier to detect than milder atherosclerosis, which is the primary limitation of clinical screening tests for PAD. More studies, particularly of people with mild and moderate PAD are needed to continue to build the body of evidence to support best practice in this area.
When PAD is identified or suspected from clinical tests, a laboratory test, duplex ultrasound is ideally indicated to determine the extent of the disease and act as a baseline for monitoring. Duplex ultrasound does not supersede clinical tests but complements the clinical picture of the individual's disease manifestation, and thereby informs clinical decision making for best practice.
Professor Robert Hinchliffe, vascular surgeon, and lead in the IWGDF, speaks clearly in this video about PAD diagnosis with bedside tests combined with laboratory tests.
Case study - significant PAD with no visual signs
A 69-year old woman, with well-controlled diabetes of 12 years, was referred for leg pain. She presented as fit, active and slim, a non-smoker and a regular walker but left calf pain was limiting her activity, which was worse with hills and relieved by rest. Her mother died at 71 of a cerebrovascular accident.
Results: Peripheral vascular results were indicative of PAD with all pulses non-palpable, monophasic waveforms, and toe pressures of left 60 and right 85 mm Hg. Colour duplex doppler testing revealed left iliac stenosis of > 75% and left calf stenosis.
The monophasic dopplers were a red flag for the presence of PAD. The difference in toe pressures of 15 mm Hg fit with the duplex ultrasound results of significant stenoses affecting her symptomatic side.
Outcome: Modifiable risk factors for PAD were addressed to reduce her risk of cardiovascular disease, including reviewing the doses of her triad of medications- statin, antihypertensive and adding an antiplatelet. Vascular surgery to address her iliac stenosis was indicated. She continues to exercise regularly to the tolerance of her claudication pain pre-surgery.
Question 1. Visual signs of skin colour, nail changes and loss of hair growth are valid as screening tests for PAD.
True or false?
Question 2. Capillary filling time is a handy clinical skill and a valid test for arterial supply status.
True or false?
Question 3. The presence of pulses means that PAD is not present, and the vascular assessment can be terminated.
