Practice Easily missed?

Acute leg ischaemia

BMJ 2013; 346 doi: http://dx.doi.org/10.1136/bmj.f2681 (Published 08 May 2013) Cite this as: BMJ 2013;346:f2681
  1. Stephen Brearley, consultant surgeon
  1. 1Whipps Cross University Hospital, London E11 1NR, UK
  1. vascusurg{at}btconnect.com

A 55 year old man consulted his general practitioner complaining of persistent pain in his left leg for three days and a numb feeling in the foot. He was taking treatment for hypertension, had a history of low back pain, and was a smoker of 20 cigarettes a day. His foot looked normal, but sensation seemed mildly reduced. The general practitioner noted a weak dorsalis pedis pulse. A diagnosis of sciatica was made, diclofenac was prescribed, and the patient was invited to return a week later if no better. Six days later he presented to a local emergency department because of intolerable pain and was found to have a profoundly ischaemic left leg necessitating an above knee amputation.

Missed diagnoses of acute leg ischaemia, as in the case above, are common.1 2 An analysis of data held by the NHS Litigation Authority (NHSLA), the Medical Defence Union (MDU), and the Medical Protection Society (MPS) identified 224 cases of acute leg ischaemia leading to limb loss over a 10 year period,1 in all of which litigation had been initiated. Fifty one cases in which there had been delay in detecting and treating acute limb ischaemia were reported to the National Reporting and Learning System (NRLS) between 2003 and 2010.2 I have written almost 30 medicolegal reports on cases in which there were allegations—usually against general practitioners or casualty officers—of a negligent delay in diagnosing acute leg ischaemia, often resulting in the avoidable loss of a limb.

What is acute leg ischaemia?

Leg ischaemia results from thrombotic, embolic, or traumatic arterial occlusion. It is considered to be acute if the symptoms and signs have developed over less than two weeks.3 4 The term “acute ischaemia” does not of itself imply severe ischaemia, but the survival of an acutely ischaemic limb is often in immediate jeopardy.2 The hallmarks of acute ischaemia that is limb threatening are reduced muscular power and reduced sensation in the limb.

How common is it?

In a 1996 questionnaire survey of members of the Vascular Surgical Society of Great Britain and Ireland, 86 out of 182 hospitals reported 539 episodes of acute lower limb ischaemia in a three month period.4 In this study, acute lower limb ischaemia was defined as “a previously stable limb with sudden deterioration in the arterial supply for less than two weeks.” In another study, an incidence as high as one per 7000 per annum has been quoted.5 Medicolegal data1 show that over 20 legal actions are initiated each year in the UK in relation to acute leg ischaemia, with delay in diagnosis or treatment figuring in 73% of the claims.

Why is it missed?

In the cases reported to the NRLS, the National Patient Safety Agency stated that causes of delay in detecting and treating acute limb ischaemia included diagnostic errors (such as misdiagnosis as a Baker’s cyst or disc problem, as in the case scenario), acute limb ischaemia not being recognised as a surgical emergency, and apparently inconsistent clinical diagnosis and assessment. My own clinical and medicolegal experience indicates that there is often a failure to consider a diagnosis of acute leg ischaemia at all, especially if the patient is under 60 years old (as in the case scenario). By no means all patients with acute leg ischaemia have risk factors (such as atrial fibrillation, a history of smoking, or diabetes). It should therefore be considered in the differential diagnosis of all patients presenting with leg pain of sudden onset, irrespective of age and risk factors, and all such patients should undergo an assessment of the circulation to the limb.

The extent to which acutely ischaemic legs are pale (or discoloured) or cold or exhibit diminished power or sensation is variable, and subtle changes can be missed (as in the case above) if the examination is cursory. An error encountered in almost all cases of missed acute leg ischaemia, however, is that one or more doctors have purported to feel pulses that could not possibly have been present. Pulse palpation is an unreliable physical sign, with false positive palpation occurring in 14% of observations carried out by non-specialists.6 A “weak” or “faint” ankle pulse, or one which the doctor “thinks” he or she can feel, is probably not present at all (as in the case history above). A simple rule will protect against this common error: “If you can feel a pulse you can count it; if you cannot count it, you are not feeling it.”

Why does it matter?

Delay in diagnosis or referral was the sole or the principal cause of amputation in 59% of the patients identified from medicolegal data.1 The interval between the onset of symptoms and irretrievable damage to the leg is variable but may be as little as six hours.2 7 Acute leg ischaemia is associated with an amputation rate of 13% and a mortality of 10%.8 Both are increased by delay in diagnosis and treatment.8

How is it diagnosed?

Acute leg ischaemia can only be diagnosed if it is included in the differential diagnosis of leg pain of recent onset. It should be considered in patients of all ages. Although usually encountered in patients over 60 years old, rare disorders (such as popliteal entrapment syndrome, cystic adventitial disease, and thrombophilias) may occasionally lead to its development in much younger individuals.

In all patients presenting with leg pain of sudden onset, look for the symptoms and signs of limb threatening ischaemia as characterised by the “six Ps” (see box).The patient will always have persistent pain and the ankle pulses will always be absent. The other Ps may or may not be present, depending on severity, and if present may be subtle (as in the case above). The presence or absence of risk factors for peripheral arterial disease is of limited usefulness. Limb threatening ischaemia may develop in individuals who have no known risk factors and are well under the age of 60.

Leg ischaemia—the “6 Ps”

  • Pain—Always present, persistent

  • Pallor or cyanosis or mottling*

  • Perishing with cold (poikilothermia)*

  • Pulselessness—Always present. Can you count it?

  • Paraesthesia or reduced sensation or numbness*

  • Paralysis or reduced power*

  • *May be subtle. Compare left and right legs

The presence of acute leg ischaemia can be quickly, simply, and reliably confirmed or ruled out by measuring the ankle blood pressure with a pocket Doppler machine and a blood pressure cuff.9 The absence of Doppler signals indicates a threatened limb, and the patient requires emergency referral to a vascular centre. Doppler assessment can be quickly learnt, is reproducible, and is easier than many other procedures routinely carried out in primary care (such as funduscopy). Pocket Doppler machines are cheap (approximately £300).

How is it managed?

If a patient has leg pain of recent onset and has impalpable pulses, immediate referral to a vascular surgical unit is mandatory. The management undertaken there will depend on the immediacy of the threat to the survival of the limb. The key clinical indicators of this are the presence and severity of reduced muscular power and reduced sensation. Depending on the urgency of the situation, the vascular unit may carry out imaging studies of the arteries supplying blood to the leg (duplex ultrasound, magnetic resonance angiography, computed tomographic angiography or intra-arterial angiography) as a basis for planning treatment. The options for treatment comprise endovascular procedures (angioplasty, thrombectomy, and intra-arterial thrombolysis) and surgery (embolectomy and bypass).7 In an immediately threatened limb, emergency surgery will be required. Regrettably, some patients present with limbs that are already dead (profound paralysis and numbness, fixed mottling of the skin). In this situation revascularisation may be not merely futile but harmful, and primary amputation is necessary.8

Notes

Cite this as: BMJ 2013;346:f2681

Footnotes

  • This is one of a series of occasional articles highlighting conditions that may be more common than many doctors realise or may be missed at first presentation. The series advisers are Anthony Harnden, university lecturer in general practice, Department of Primary Health Care, University of Oxford, and Richard Lehman, general practitioner, Banbury. To suggest a topic for this series, please email us at easilymissed@bmj.com.

  • Contributors: The article’s content was developed in discussion with J Murray Longmore, and the first draft was revised in the light of comments from Longmore.

  • Competing interests: I have read and understood the BMJ Group policy on declaration of interests and have no relevant interests to declare.

  • Provenance and peer review: Commissioned; externally peer reviewed.

  • Patient consent: Patient consent not required (patient anonymised, dead, or hypothetical).

References