Anatomic breakdown of the leg into its various anatomic components is the basis of a sound differential diagnosis (Table 44). Before that, however, one should determine if the pain is actually originating from the hip or if it is the result of knee joint disease. Diagnosis of these must be considered (see pages 226 and 274).
Beginning with the skin, consider herpes zoster and various dermatologic conditions. In the subcutaneous tissue, one encounters cellulitis and occasionally filariasis, which may produce a similar picture. Beneath this layer, the muscle and fascia suggest numerous causes of leg pain. There may be hematomas of the muscle, trichinosis or cysticercosis, nonarticular rheumatism, or fibromyositis. Muscle cramping from low sodium or other electrolyte disturbances must be considered.
The superficial and deep veins are the site of thrombophlebitis, a prominent cause of leg pain. The arteries may be involved by emboli (from auricular fibrillation, acute myocardial infarction, and subacute bacterial endocarditis), thrombosis (especially in Buerger disease and blood dyscrasias), and vasculitis (from arteriosclerosis and collagen diseases). Acute trauma to the artery or veins may cause pain. As usual, when one moves centrally along the arterial pathways additional causes of pain come to mind. Leriche syndrome and dissecting aneurysm must be considered. When superficial or deep infections of the leg spread to the lymphatics, lymphangitis is important in the differential.
The nerves may be involved locally, centrally, or systemically. Buerger disease, cellulitis, and osteomyelitis may involve the nerve locally. Neuromas may occasionally cause focal pain in the distribution of the nerve involved. More important are the central causes of nerve pain in the limbs. Probably herniated discs of the lumbar spine account for most of these cases, but Pott disease, lumbar spondylosis (osteoarthritis?), metastatic and primary tumors, multiple myeloma, fractures, spondylolisthesis, and osteomyelitis of the spine all may compress the cauda equina and cause pain in the lower limbs.
Pelvic tumors, endometriosis, and sciatic neuritis are, in a sense, “central” causes of leg pain, and all patients deserve a rectal and pelvic examination when the diagnosis is obscure. Pelvic inflammatory disease and obturator hernias may rarely involve the obturator nerve. Meralgia paresthetica from diabetes mellitus and other causes must be considered in thigh pain and in causalgia. Finally, the thalamic syndrome and diseases of the cervical spine must be considered. Dissecting the limb layer by layer, we finally reach the bone, which suggests osteomyelitis, bone tumors, Osgood–Schlatter disease, tuberculous osteomyelitis, and Paget disease. Joggers may experience shin splints, stress fractures, or compartment syndrome. Gymnasts, ballet dancers, and skiers experience patella–femoral problems. For leg pain originating in the joints, see page 274.
Systemic diseases that may involve the nerves causing pain in the legs include tabes dorsalis, periarteritis nodosa, diabetes mellitus, metabolic and nutritional neuropathies, and blood dyscrasias.
Approach to the Diagnosis
The approach to the diagnosis of leg pain involves numerous ancillary examinations that one may not routinely do. Leg pain that is sudden in onset should be considered osteomyelitis until proven otherwise. Thus, arterial pulses must be checked all the way up. One should look for a positive Moses or Homans sign. Straight leg raising (SLR) and meticulous mapping of sensory changes are valuable. The SLR sign may be negative and the patient could still have a herniated disc higher up. Thus, a femoral stretch test is done1 and when positive suggests a herniated disk at L2–3 or L3–4. Patients with pain in the hip should always be examined for greater trochanter bursitis, a common condition (page 226). Edema associated with phlebitis or atrophy associated with a herniated disc can be detected only with careful measurement of the calf and thigh. Deep vein thrombophlebitis can be diagnosed by ultrasonography or impedance plethysmography. Arterial circulation is best evaluated with an ultrasound flow study. Venography and arteriography may be necessary if plain x-ray films are unremarkable. One should almost always x-ray the spine, hips, knee joints, and, in difficult cases, the entire legs. Pain that is precipitated by walking suggests peripheral arteriosclerosis, but spinal stenosis is also possible.
Other Useful Tests
Complete blood count (CBC) (infection)
Sedimentation rate (infection, arthritis)
Chemistry panel (gout, diabetes, etc.)
Serum protein electrophoresis (multiple myeloma)
Electromyogram (EMG) and nerve conduction velocity (NCV) (radiculopathy, neuropathy)
Computed tomography (CT) scan or magnetic resonance imaging (MRI) of the lumbar spine (herniated disc, etc.)
Lyme titer (Lyme disease)
Bone scan (osteomyelitis)
Ankle–brachial index (Leriche syndrome, arteriosclerosis)
Iodine 125-radioactive-labeled fibrinogen leg scanning (thrombophlebitis)
Arthrocentesis (gout, pseudogout, etc.)
MRI (stress fractures)
CT angiography or MRA (arteriosclerosis)
Table 44 Leg Pain
Case Presentation #62
A 36-year-old white female cashier developed acute pain in her right calf 2 hours before admission. She gives a history of taking birth control pills for several years.
Question #1. Considering the anatomy of the area, what would be your differential diagnosis?
Examination revealed that she had excellent peripheral pulses, but there was 2+ pitting edema of the right leg and a positive Homans sign.
Question #2. What is your diagnosis now?
(See Appendix B for the answers.)
Numerous disorders cause leukocytosis. How can we recall all possibilities in the differential? The mnemonic VINDICATE would seem to be the answer.
V—Vascular would call to mind myocardial infarction, pulmonary infarction, cerebral vascular accident, and thrombophlebitis.
I—Inflammation should bring to mind bacterial infections anywhere in the body, but especially septicemia. Parasitic infections would cause an eosinophilia. Severe systemic fungal infections would also cause leukocytosis. Viral infections are not usually associated with leukocytosis but there are notable exceptions, such as infectious mononucleosis.
N—Neoplasm would of course prompt the recall of acute and chronic leukemias and agnogenic myeloid metaplasia.
D—Degenerative disorders do not prompt the recall of any important disorder.
I—Intoxication would bring to mind various drugs that are associated with a leukocytosis, such as lithium, corticosteroids, and lead.
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