Parkinson’s disease most commonly begins with a tremor in one hand but can also cause limb stiffness or slowness of movement without tremor. Or, perhaps, someone else may notice that you’re not swinging your arm normally as you walk.

Symptoms of Parkinson’s disease are separated into three categories: primary motor symptoms, secondary motor symptoms and nonmotor symptoms. Here’s what you need to know:

Primary Motor Symptoms

Resting tremor: This happens when a body part on one side of the body (usually a hand or foot) shakes slightly when you’re not using it (hence “resting”). The tremor usually stops when you start doing something with that hand or other body part.

Bradykinesia: The definition of bradykinesia is slow and small movement. You may not be able to walk at your normal pace, step size might be smaller or you may perform repeated movements more slowly (think tapping your fingers on a table). Some examples of this are:

• Freezing of gait: This is when you attempt to take a step forward and suddenly feel as though you can’t, as though your foot is “stuck” to the floor. Sometimes it’s temporary, and once you do start walking, the freezing goes away.

• A “mask” face: Possibly as a result of a combination of rigidity and bradykinesia, your facial expression may look flat or masklike. What happens is your facial muscles lose some of their involuntary movements.

• Micrographia (smaller handwriting): The result of bradykinesia, your ability to perform repetitive motions decreases, leading to smaller, more cramped handwriting.

Rigidity: This occurs when muscles remain tense rather than contracting and relaxing as normal, and is often described by patients as stiffness. Combined with bradykinesia, it’s what causes such phenomena as walking without swinging your arms in a normal motion.

Postural instability/poor balance: This symptom occurs when you find it hard to remain upright, either when standing or as you rise from a chair. It may feel as though you’re tipping backward. You may find it harder to make a quick turn or pivot without tending to fall.

Nonmotor Symptoms

Constipation: If you have difficulty with bowel movements that can’t be explained by other factors — a diet low in fiber or water, or the use of certain medications — it can be a sign of Parkinson’s disease.

Hyposomia: This is a loss of some of your sense of smell, and it’s common in Parkinson’s (though it may also be overlooked as an early symptom). This may also secondarily affect the sense of taste, given that odor is heavily involved in flavor. One theory is that the same clumping of the protein alpha-synuclein that occurs in the part of the brain that controls dopamine receptors also happens in the olfactory bulb, which controls sense of smell.

REM sleep behavior disorder: This is when people seem to “act out” their dreams. You may thrash around in bed in your sleep or even fall out of bed.

Mood disorders: Psychological issues, such as depression and anxiety, can be an early sign of Parkinson’s disease and may arise long before motor symptoms do.

Urinary frequency/urgency: Patients with Parkinson’s disease often feel the need to urinate more urgently, even when their bladder is not very full. Getting to the bathroom quickly is often complicated by the movement problems mentioned above.