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Long-established treatments for essential tremor, such as medication and deep brain stimulation surgery, have been joined by a leading-edge technique called focused ultrasound. This incision-free procedure aims sound waves at a spot deep in the brain responsible for tremors. While scientists study ultrasound's long-term effects, the procedure is currently used to treat shakiness on only one side of the body. Other common causes of tremor include Parkinson's disease, caffeine, alcohol withdrawal, anxiety, and fatigue.

People sometimes experience a sudden tingling or numbness in the feet or hands that goes away. But if the problem keeps occurring, followed by painful or burning sensations, this could be a sign of small-fiber neuropathy. While not life-threatening, small-fiber neuropathy should always be checked out, as it could be a symptom of something more serious.

Though decades of research have suggested risk factors for amyotrophic lateral sclerosis, a specific cause remains unknown. New research studied professional football players and found that they had a much higher risk of developing ALS than men in the general population, though the study was only observational.

Millions of people have tinnitus, a condition where a person hears a sound inside the head that does not come from any external source. There are many possible causes and no cure, but there are ways to ease the symptoms, one of which is sound therapy, which uses external sound to alter a person's perception of or reaction to tinnitus.

Essential tremor causes involuntary shaking, most often in the hands, head and voice. It may be an inherited condition and is different from another well-known tremor disorder called Parkinson's disease. There is no cure, but symptoms can be managed through medication and lifestyle changes.

Ask the doctors

Q. My friend was recently diagnosed with fibromyalgia, but it seems like she might be imagining her symptoms. Is fibromyalgia a real condition?

A. The short answer to your question is yes. Fibromyalgia is a real condition that affects some four million Americans. It's a chronic pain syndrome that experts believe may be caused by a malfunctioning nervous system. Researchers using magnetic resonance imaging to examine the brains of people with fibromyalgia have found abnormalities in the part of the brain that processes pain signals from the body. It appears that this part of the brain is essentially boosting the intensity of normal pain signals, potentially causing the body to feel pain without a physical cause.

The potential causes may be hard to pin down. Here are some of the most common ones � and what to do about them.

Sometimes it's easy to know why a particular part of your body is itchy. Maybe you have a bug bite, allergies, or a visible skin condition such as eczema. It's harder to know the cause when there's nothing obvious behind all-over, generalized itching. "It's the most common skin complaint in people over age 65," says Dr. Kenneth Arndt, a dermatologist and former medical editor of the Harvard Special Health Report Skin Care and Repair.

Potential causes

Generalized itching has many potential triggers. One is aging. "The skin barrier doesn't work as well as it used to, and things that may not have irritated you before may now be absorbed in the skin and cause itching," Dr. Arndt explains. "The skin also develops a somewhat impaired immune response, a reduction in fat and blood flow, and altered sensory perception, making it more prone to itching."

On call

Q.ÌýMy feet tingle or feel numb like they are asleep at times, mostly when I am in bed or with my legs elevated. What causes that?

A.ÌýThe symptoms you describe may be related to peripheral neuropathy, which is nerve damage that affects multiple nerves leading out from the spinal cord to the arms and legs. Symptoms are often equal in both feet. If only one foot, or part of a foot, is affected, this suggests compression of an individual nerve.