Tremors are a form of movement disorder characterized by involuntary rhythmic motion of the hands, face, head, voice, legs or torso. The speed and breadth of tremors vary, as do the provocative events that stimulate them. Causes of tremors include injuries, metabolic disturbances and inherited or acquired conditions that adversely affect the areas of the brain that control movement.
Essential Tremor
The National Institute of Neurological Disorders and Stroke reports that essential tremor, also known as benign essential tremor, is the most frequent cause of this symptom. The disorder most commonly begins after age 40, but may affect children and adults of any age. Essential tremor often runs in families. "The Merck Manual" reports that approximately 60 percent of people with essential tremor have affected family members.
Essential tremor most frequently manifests in the forearms and hands. Less commonly, the voice and head may be involved. The tremor begins gradually and may progress with time. Both sides of the body are characteristically affected. Purposeful movement provokes essential tremor. People with hand tremors often have difficulty with tasks such as reaching for an object, holding a glass, trying to insert a key into a lock or attempting to write. While severe essential tremor poses physical challenges, the disorder is not associated with the development of other neurological or physical problems and is not life-threatening.
Systemic Metabolic Abnormalities
Disorders that significantly disturb the body's metabolic balance can provoke tremors, according to "The Merck Manual." Metabolic causes of tremors include uremic encephalopathy associated with kidney failure; hepatic encephalopathy associated with liver failure; hypoglycemia, or low blood sugar; hyperthyroidism, or an overactive thyroid; oxygen deprivation of the brain; pheochromocytoma, a tumor that produces excessive adrenalin, and hyperparathyroidism, or overactive parathyroid glands.
Tremors associated with metabolic abnormalities are of the postural variety. Holding the affected limbs in a fixed position, such as extending the arms out in front of the body, typically provokes maximal tremor activity. The Cleveland Clinic notes that altered mental status or function often accompanies metabolic tremors. Correction of the underlying metabolic disturbance often corrects this form of tremor.
Parkinson's Disease
Parkinson's disease is a chronic, gradually progressive movement disorder characterized by posture and balance disturbances, rigidity, difficulty initiating movement and tremors. "The Merck Manual" reports that an isolated resting tremor is frequently the first symptom of Parkinson's disease. Parkinson's disease tremors are characteristically slow and abate with purposeful movement. The hands and arms are most commonly affected, with one side of the body initially involved.
Parkinson's disease characteristically causes symptoms outside of the motor control system, including sleep disturbances, low blood pressure, constipation, urinary bladder problems, seborrheic dermatitis, depression and dementia.
