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Limb pain may affect all or part of an extremity (for joint pain, see page Pain in and Around Joints). Pain may be constant or intermittent, and unrelated to motion or precipitated by it. Accompanying symptoms and signs often suggest a source.
Musculoskeletal injuries and overuse are the most common causes of pain in a limb but are readily apparent by history. This discussion covers extra-articular limb pain unrelated to injury or strain. Pain that is in only one or more joints is discussed elsewhere (see page Pain in and Around Joints). There are many causes (see Table: Some Causes of Nontraumatic Limb Pain) but the most common are the following:
Uncommon but serious causes that require immediate diagnosis and treatment include
Some Causes of Nontraumatic Limb Pain
It is important to exclude acute arterial occlusion.
History of present illness should address the duration, intensity, location, quality, and temporal pattern of pain. Recent injury, excessive and/or unusual use, and factors that worsen pain (eg, limb movement, walking) and relieve pain (eg, rest, certain positions) should be noted. Any associated neurologic symptoms (eg, numbness, paresthesias) should be identified.
Review of systems should seek symptoms of possible causes, including back or neck pain (radiculopathy), fever (infections such as osteomyelitis, cellulitis, or deep soft-tissue infection), dyspnea (DVT with pulmonary embolism, MI), and chest pain or sweating (cardiac ischemia).
Past medical history should identify known risk factors, including cancer (metastatic bone tumors); immunocompromising disorders or drugs (infections); hypercoagulable states (DVT); diabetes (peripheral vascular disease with limb ischemia); peripheral vascular disease, hypercholesterolemia, and/or hypertension (acute or chronic ischemia); osteoarthritis or RA (radiculopathy); and prior injury (complex regional pain syndrome). Family and social history should address family history of early vascular disease and cigarette smoking (limb or cardiac ischemia) and illicit use of parenteral drugs (infections).
Vital signs are reviewed for fever (suggesting infection) and tachycardia and/or tachypnea (compatible with DVT with pulmonary embolism, MI, and infection with sepsis).
The painful limb is inspected for color, edema, and any skin or hair changes, and palpated for pulses, temperature, tenderness, and crepitation (a subtle crackling sensation indicating soft-tissue gas). Strength, sensation and deep tendon reflexes are compared between affected and unaffected sides. Systolic BP is measured in the ankle of the affected extremity and compared with systolic BP of an arm; the ratio of the two is the ankle-brachial index.
Sudden, severe pain
Signs of acute limb ischemia (eg, coolness, pallor, pulse deficits, delayed capillary refill)
Dyspnea, chest pain, and/or sweating
Signs of systemic toxicity (eg, delirium, tachycardia, shock, pallor)
Crepitation, tenseness, foul discharge, bullae, necrosis
Risk factors for deep venous thrombosis
It can be helpful to categorize patients by acuity of symptoms and then further narrow the differential diagnosis based on presence or absence of findings of
Sudden, severe pain suggests acute ischemia or acute radiculopathy (eg, from sudden disc herniation). Acute ischemia causes generalized limb pain and manifests with weak or absent pulse, delayed capillary refill, coolness, and pallor; ankle-brachial index is typically < 0.3. Such vascular signs are absent with radiculopathy, in which pain instead follows a dermatomal distribution and is often accompanied by back or neck pain and diminished deep tendon reflexes. However, in both cases, weakness may be present. Acute ischemia due to massive venous thrombosis (phlegmasia cerulea dolens) usually causes edema, which is not present in ischemia due to arterial occlusion.
In subacute pain (ie, of 1 to a few days' duration), redness and tenderness, often accompanied by swelling, and/or warmth, suggest an inflammatory cause. If these findings are focal or circumscribed, cellulitis is likely. Generalized, circumferential swelling is more suggestive of DVT or, much less commonly, deep tissue infection. Patients with a deep tissue infection typically appear quite ill and may have blisters, necrosis, or crepitation. Findings in DVT vary widely; swelling and warmth may be minimal or absent. Neurologic findings of weakness, paresthesias, and/or sensory abnormalities suggest radiculopathy or plexopathy. If neurologic findings follow a dermatomal pattern, radiculopathy is more likely.
Chronic pain can be difficult to diagnose. If neurologic findings are present, causes include radiculopathy (dermatomal distribution), plexopathy (plexus distribution), neuropathy (stocking-glove distribution), and complex regional pain syndrome (variable distribution). Complex regional pain syndrome should be suspected if vasomotor changes (eg, pallor, mottling, coolness) are present, particularly in those with previous injury to the affected extremity. Myofascial pain syndrome causes no neurovascular abnormalities and classically manifests with a palpably tense band of muscle in the area of pain, and pain may be reproduced by pressure on a trigger point near but not overlying the area of pain. In those with essentially no clinical findings, cancer and osteomyelitis should be considered, particularly in those with risk factors.
Intermittent pain occurring consistently with a given degree of exertion (eg, whenever walking > 3 blocks) and relieved with a few minutes of rest suggests peripheral arterial disease. Such patients typically have an ankle-brachial BP index of ≤ 0.9; an index ≤ 0.4 indicates severe disease. Those with peripheral arterial disease may have chronic skin changes (eg, atrophy, hair loss, pale color, ulceration).
Cellulitis, myofascial pain, painful polyneuropathy, and complex regional pain syndrome can often be diagnosed clinically. Testing (see Table: Some Causes of Nontraumatic Limb Pain) is usually necessary for other suspected causes of pain.
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