ARM PAIN

ARM PAIN: Excerpt from Differential Diagnosis in Primary Care

An anatomic breakdown of the arm into its components is the key to a sound differential diagnosis in arm pain. Pain may be referred from more proximal portions of the extremity such as the shoulder (e.g., bursitis) or brachial plexus (e.g., cervical rib), so these areas must also be examined.

ARM PAIN

Beginning with the skin and subcutaneous tissue, one recalls herpes zoster, cellulitis, contusions, and a variety of dermatologic conditions that should be obvious. Weber–Christian disease, which usually affects the thighs, is more obscure. Rheumatoid and rheumatic nodules may occur on the skin and are, of course, painful. Beneath the skin the muscles, fascia, and bursae are frequent sites of inflammation and trauma. Contusions, rupture of the ligaments, and bursitis (particularly tennis elbow) are common acute traumatic conditions (bursitis, however, is more likely the result of chronic strain). Inflammatory lesions of the muscles include epidemic myalgia, trichinosis, nonarticular rheumatism, and dermatomyositis. Muscle cramping from hypocalcemia or other electrolyte disturbances must be considered in the differential diagnosis of arm pain.

The superficial and deep veins are the site of thrombophlebitis and hemorrhage, both prominent causes of arm pain. The arteries may be involved by emboli (from auricular fibrillation, myocardial infarction, and subacute bacterial endocarditis), thrombosis (especially in Buerger disease and blood dyscrasias like sickle cell anemia), and vasculitis (periarteritis nodosa is one example). Acute trauma to the artery may cause pain. When one moves centrally along the arterial pathways, additional causes of pain come to mind. For example, dissecting aneurysms or acute subclavian steal syndrome may cause severe pain down the arm, but pain is referred to the arm from a myocardial infarct as well. When superficial or deep infections of the arm spread to the lymphatics, lymphangitis may develop and cause arm pain.

The nerves may be a source of pain, both centrally and locally. Buerger disease, cellulitis, and osteomyelitis may involve the nerve locally. Neuromas may cause focal pain in the distribution of the involved peripheral nerve. Carpal tunnel syndrome, which may be caused by rheumatoid arthritis, amyloidosis, acromegaly, hypothyroidism, or multiple myeloma, may compress the median nerve (and occasionally the ulnar nerve) to cause pain in the hand and even up the arm. Moving up the nerve pathways, another frequent spot for nerve compression is the brachial plexus. Pancoast tumors, cervical ribs, and the scalenus anticus syndrome may be the cause of arm pain originating the plexus.

The cervical nerve roots may be compressed by diseases of the spine and spinal cord. A herniated disc, cervical spondylosis, metastatic carcinoma, tuberculosis of the spine, multiple myeloma, and cord tumors (e.g., meningiomas, neurofibromas, and ependymomas) are the most notable. Syringomyelia and tabes dorsalis are other sources of arm pain that originate in the spinal cord. Moving up the cord to the brainstem, one recalls the thalamic syndrome (usually caused by occlusion of the thalamogeniculate artery) as a cause of pain in the arm.

The bone and joints are deeper in the arm. They prompt the diagnosis of osteomyelitis, primary and metastatic bone tumors, and diseases of the joints such as osteoarthritis, rheumatoid arthritis, gout, gonococcal arthritis, and Reiter syndrome. A more extensive discussion of joint disorders can be found on page 343. Systemic diseases that cause arm pain from peripheral nerve involvement include diabetes mellitus (with ischemic neuropathy), periarteritis nodosa, and macroglobulinemia. Sickle cell anemia may also cause an ischemic neuropathy.

Approach to the Diagnosis

The association of other symptoms and signs found on a good history and physical examination is most important in pinpointing the diagnosis. Thus, arm pain with tenderness and limitation of motion at the elbow suggests tennis elbow, gout, or rheumatoid arthritis. Arm pain with loss of sensation in the distribution of the median nerve suggests carpal tunnel syndrome. Injection of lidocaine into bursa or trigger points may be diagnostic.

The laboratory workup should include x-rays of the involved area and of the cervical spine, especially if there is a radicular distribution of the pain. If there are focal neurologic signs, a neurologist should be consulted before ordering an MRI: A cervical rib will not be missed in this way. An ECG and myocardial enzymes may be necessary to exclude a myocardial infarct, and an exercise tolerance test will help exclude coronary insufficiency. Arteriogram, phlebogram, lymphangiogram, electromyogram (EMG) with nerve conduction studies, myelogram, and nerve blocks will be necessary in specific cases.

Other Useful Tests

1. Stellate ganglion block (Reflex sympathetic dystrophy)
2. Dermatomal somatosensory evoked potentials (DSEPs) (neuropathy, radiculopathy, demyelinating disease)
3. Arthritis panel
4. Chest x-ray (Pancoast tumor)
5. MRI of shoulder (torn rotator cuff).

ARM PAIN, LOCAL CAUSES

Book Source Details

• Book Title: Differential Diagnosis in Primary Care
• Author(s): R. Douglas Collins
• Year of Publication: 2007
• Copyright Details: Differential Diagnosis in Primary Care, Copyright © 2007 Lippincott Williams & Wilkins.

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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.

More About This Book: Title: Differential Diagnosis in Primary Care Authors: R. Douglas Collins Publisher: Lippincott Williams & Wilkins Copyright: 2007 ISBN: 0-7817-6812-8

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