Most skin conditions should be easily diagnosed by inspection. A Wood lamp inspection would assist in the diagnosis of tinea capitis. A potassium hydroxide (KOH) preparation of scraping may be necessary. Skin biopsy will diagnose other skin disorders. A sedimentation rate and biopsy of the superficial temporal artery will diagnose temporal arteritis. If occipital nerve entrapment is suspected, a nerve block should be done to confirm the diagnosis. X-rays of the skull and a magnetic resonance imaging (MRI) may be necessary, but a neurologist should be consulted before ordering expensive diagnostic tests.

To diagnose scoliosis, have the patient bend over, and there will be asymmetry in the height of the scapulae (Adam test). Most causes of scoliosis will require only an x-ray of the spine to clarify the diagnosis. An orthopedic consult should be obtained before any further workup. Be sure to measure the leg length. If there are objective neurologic signs, a neurologist should be consulted. A bone scan, MRI, or computed tomography (CT) scan may be necessary in difficult diagnostic problems.

The neurologic examination will help to determine the location of the lesion. Peripheral neuropathy presents with diffuse distal loss of sensation to all modalities. Nerve root involvement will present with sensory loss in a radicular distribution; spinal cord involvement will be associated with a sensory level. Sensory loss to pain and temperature on one side of the face and the opposite side of the body is typical of posterior inferior cerebellar artery occlusion. If there is only loss of vibratory and position sense, look for pernicious anemia or a cerebral tumor.

The workup for peripheral neuropathy and entrapment syndromes will include nerve conduction velocity (NCV) tests and EMGs. An MRI and CT scan can be done if brain and spinal cord pathology is suspected, but a neurologist should be consulted first. If a cerebrovascular disease is suspected, Doppler ultrasound and magnetic resonance angiography (MRA) may be necessary as well. Ultimately, four-vessel cerebral angiography may be indicated.

The approach to ruling out various causes is most often clinical, provided x-rays of the shoulder and cervical spine have negative findings. If a torn rotator cuff is strongly suspected, an MRI or arthrogram should be done. In the classical case of subacromial bursitis (recently called impingement syndrome), in which passive movement is much less restricted than active movement and a point of maximum tenderness can easily be located, lidocaine and steroid injections into the bursa (at the point of maximum tenderness) may be done without x-rays. Cervical root blocks, stellate ganglion blocks for shoulder–hand syndrome, and aspiration and injection of the shoulder joint with lidocaine and steroids may also be useful in establishing the cause. Adson maneuvers will help to establish the diagnosis of scalenus anticus syndrome, but the clinician must bear in mind that there are many false positives for this test and the job is not finished until tests for pectoralis minor and costoclavicular compression are done. The history will help to diagnose systemic causes, but checking for dermatomal hyperalgesia or hypalgesia and other sensory changes will be most helpful in diagnosing disease of the cervical spine. Remember that a negative cervical spine x-ray does not rule out a herniated disk. If the pain is increased by pressure on the top of the head or by coughing and sneezing, then a herniated disk must be ruled out by an MRI.

Smear and culture of the lesion are most important, although a skin biopsy is sometimes necessary. Serologic tests or cultures on special media are necessary to diagnose fungi and parasites.

A biopsy or excision is the best approach to the diagnosis. If a systemic disease is suspected because of a lesion, appropriate studies for these are listed below.

The workup for diffuse pigmentation involves ruling out hemochromatosis, hepatobiliary disease, and Addison disease with appropriate tests for these disorders (see Appendix A) and using the expertise of a dermatologist in the cases of patchy pigmentation.

If myxedema is suspected, a thyroid-stimulating hormone (TSH) test and FT₄ test can be ordered. If scleroderma is suspected, order an ANA, anticentromere antibody titer, or a skin biopsy. Urine for porphyrins will help to identify porphyria. Carcinoid syndrome can be identified by a urine test for 5-hydroxyindole acetic acid (HIAA).

The differential diagnosis of skin ulcers may be approached with anatomy as the basic science, particularly if the ulcer is on one of the legs. Beginning with the skin itself and applying the mnemonic MINT, one can recall the following:

Now visualize the structure beneath the skin. The arteries suggest arteriosclerosis and diabetic ulcers; the veins prompt the recall of varicose ulcers or postphlebitic ulcers; the nerves suggest trophic ulcers of tabes dorsalis, syringomyelia, and peripheral neuropathy; and the bone suggests osteomyelitis (e.g., staphylococcal, tuberculosis) that penetrates the skin.

In contrast to the method described above, a somewhat more complete differential diagnosis may be developed with the mnemonic VINDICATE.

Infections can be further elucidated by working from the smallest organism to the largest. Beginning with viruses, herpes simplex, and lymphogranuloma is suggested. Bacteria remind one of tuberculosis, tularemia, leprosy, and cutaneous diphtheria. Spirochetes suggest syphilis and yaws. Parasites identify leishmaniasis and amebiasis cutis. The rest are fungal and include actinomycosis, blastomycosis, sporotrichosis, and cryptococcosis.