CHAPTER 105

Diagnosis of Brain, Spinal Cord, and Nerve Disorders

A neurologic examination can detect disorders of the brain, spinal cord, and nerves in other parts of the body (peripheral nerves, which include motor and sensory nerves). This examination can also help detect muscle disorders because muscle contraction depends on stimulation by a nerve.

The two main components of a neurologic examination are the medical history and the physical examination (including mental status evaluation). If necessary, diagnostic procedures are done to confirm the diagnosis or exclude other possible disorders.

A neurologic examination differs from a psychiatric examination, which focuses on a person’s behavior. However, the two examinations overlap somewhat because abnormal behavior often provides clues about the brain’s physical condition.

History

Before doing a physical examination, doctors interview the person. Doctors ask the person to describe current symptoms:

What they are like precisely

Where and how often they occur

How severe they are

How long they last

What makes symptoms worse

What relieves symptoms

Whether daily activities can still be done

The person is also asked about past or present illnesses and past operations, serious illnesses in close blood relatives, allergies, and drugs currently being taken. Questions about work, social contacts, and travel may be asked to find out whether the person has been exposed to unusual infections or toxins. In addition, doctors may ask whether the person has had work-related or home-related difficulties, such as loss of a loved one, because such circumstances may affect the person’s health and ability to cope with illness. Other questions are asked to identify any symptoms that the person may have overlooked or thought unimportant when describing the main problem.

Physical Examination

When a neurologic disorder is suspected, doctors usually evaluate all of the body systems during the physical examination, but they focus on the nervous system. They do a neurologic examination, which includes evaluation of mental status, cranial nerves, motor and sensory nerves, reflexes, coordination, balance, walking (gait), regulation of internal body processes (by the autonomic nervous system), and blood flow to the brain. Doctors may evaluate some areas more thoroughly than others depending on what type of disorder they suspect.

Mental Status: Doctors evaluate the following:

Attention

Orientation to time, place, and person

Memory

Various abilities, such as thinking abstractly, following commands, using language, and solving math problems

Mood

The evaluation consists of a series of questions and tasks, such as naming objects, recalling short lists, writing sentences, and copying shapes. The person’s answers are recorded and scored for accuracy. If the person reports feeling depressed, doctors ask if there have been any thoughts of suicide.

Cranial Nerves: There are 12 pairs of cranial nerves, which connect the brain with the eyes, ears, nose, face, tongue, throat, neck, upper shoulders, and some internal organs (see page 835). How many nerves doctors test depends on what type of disorder they suspect. For example, the 1st cranial nerve (the nerve of smell) is not usually tested when a muscle disorder is suspected, but it is tested in people recovering from serious head trauma (because smell is often lost). A cranial nerve may be damaged anywhere along its length as a result of injury, impaired blood flow, an autoimmune disorder, a tumor, or an infection. The exact site of the damage can often be identified by testing the functions of a particular cranial nerve.

Motor and Sensory Nerves: Motor nerves carry impulses from the brain and spinal cord to voluntary muscles (muscles controlled by conscious effort), such as muscles of the arms and legs. Weakness or paralysis of a muscle may indicate damage to the muscle itself, a motor nerve, or its connection to the muscle (synapse), the brain, or the spinal cord. Doctors look for abnormalities such as the following:

Tremor and other involuntary muscle movements

Muscle twitching

Decrease in muscle size (wasting or atrophy)

Increase in muscle size

Increase (spasticity or rigidity) or decrease in muscle tone

Pattern of weakness

Dexterity

The doctor inspects the muscles for size, unusual movements, tone, strength, and dexterity. A muscle wastes away (atrophies) when the muscle or the nerves supplying it are damaged or when the muscle has not been used for months for other reasons (such as being in a cast).

Muscles may move without the person meaning them to. For example, tiny muscle twitches (fasciculations) indicate nerve damage to that muscle. Other possible involuntary movements are rhythmic movements of a body part (tremor), twitches (tics), sudden flinging of a limb (hemiballismus), quick fidgety movements (chorea), or snake-like writhing (athetosis). All of these movements suggest damage in areas of the brain (called basal ganglia) that control motor coordination.

When doctors move a person’s joint passively, they note the degree of resistance to movement (muscle tone). Muscle tone that is uneven and suddenly increased (spasticity) may be due to a stroke or spinal cord injury. Muscle tone that is evenly increased (rigidity) may be due to disease of the basal ganglia, such as Parkinson’s disease. Muscle tone that is severely reduced (flaccid) immediately and temporarily after a spinal cord injury produces paralysis.

Doctors test muscle strength by asking the person to push or pull against resistance or to do maneuvers that require strength, such as walking on the heels and tiptoes or rising from a chair. Sometimes weakness is evident when a person uses one limb more than another (for example, when swinging the arms while walking or when holding the arms up with the eyes closed). Weakness that affects the muscles of the upper arms and legs more than the hands and feet may indicate a disorder that affects all of the muscles (myopathy). Myopathies tend to affect the largest muscles first. The person may have difficulty combing hair or climbing stairs.

What Is a Neurologic Symptom?

Neurologic symptoms—symptoms caused by a disorder that affects part or all of the nervous system—can vary greatly because the nervous system controls so many different body functions. Symptoms can include all forms of pain, including headache and back pain. Muscles, skin sensation, the special senses (vision, taste, smell, and hearing), and other senses depend on nerves to function normally. Thus, neurologic symptoms can include muscle weakness or incoordination, abnormal sensations in the skin, and disturbances of the senses.

Neurologic disorders can interfere with sleep, making a person anxious or excited at bedtime and thus lethargic and sleepy during the day.

Neurologic symptoms may be minor (such as a foot that has fallen asleep) or life threatening (such as coma due to stroke). The characteristics and pattern of symptoms help doctors diagnose the neurologic disorder. The following are some relatively common neurologic symptoms:

PAIN

Back pain

Neck pain

Headache

Pain along a nerve pathway (as in sciatica or shingles)

MUSCLE MALFUNCTION

Weakness

Tremor

Paralysis

Involuntary movements (such as tics)

Abnormalities in walking

Clumsiness or poor coordination

Muscle spasms

Rigidity, stiffness, and spasticity

Slowed movements

CHANGES IN SENSATION

Numbness of the skin

Tingling or a pins-and-needles sensation

Hypersensitivity to light touch

Loss of sensation for touch, cold, heat, or pain

Loss of position sense

CHANGES IN THE SPECIAL SENSES

Disturbances of smell and taste

Visual hallucinations

Partial or complete loss of vision

Double vision

Deafness

Ringing or other sounds originating in the ears (tinnitus)

OTHER SYMPTOMS

Vertigo

Loss of balance

Difficulty swallowing

Slurred speech (dysarthria)

SLEEP PROBLEMS

Difficulty falling or staying asleep

Uncontrollable leg movements

Falling asleep uncontrollably (as in narcolepsy) or sleeping too much

CHANGES IN CONSCIOUSNESS

Fainting

Confusion or delirium

Seizures

Coma

Stupor

CHANGES IN COGNITION (MENTAL ABILITY)

Difficulty understanding language or using language to speak or write (aphasia)

Poor memory

Difficulty with common motor skills, such as striking a match or combing one’s hair, despite normal strength (apraxia)

Inability to recognize familiar objects (agnosia)

Inability to sustain concentration when doing a task

Inability to distinguish right from left

Inability to do simple arithmetic (acalculia)

Poor visual-spatial comprehension (for example, being unable to draw a clock or becoming lost driving in a familiar neighborhood)

Dementia (dysfunction of several cognitive functions)

MENTAL STATUS TESTING

WHAT PEOPLE MAY BE ASKED TO DO	WHAT THIS TEST INDICATES
State the current date and place, and name specific people	Orientation to time, place, and person
Repeat a short list of objects	Attention
Recall the short list of objects after 3 to 5 minutes	Immediate recall
Describe an event that happened in the last day or two	Recent memory
Describe events from the distant past	Remote memory
Interpret a proverb (such as “a rolling stone gathers no moss”), or explain a particular analogy (such as “why the brain is like a computer”)	Abstract thinking
Describe feelings and opinions about the illness	Insight into illness
Name the last five presidents and the state capital	Fund of knowledge
Tell how they feel on this day and how they usually feel	Mood
Follow a simple command that involves three different body parts and requires distinguishing right from left (such as “put your right thumb in your left ear and stick out your tongue”)	Language comprehension
Name simple objects and body parts, and read, write, and repeat certain phrases	Ability to use language
Without looking, identify small objects held in the hand and numbers written on the palm, and discriminate between being touched in one or two places	Ability of the brain to process and interpret complex sensory information from the hand
Copy simple and complex structures (for example, using building blocks) or finger positions, and draw a clock, cube, or house	Ability to understand spatial relationships
Brush the teeth, or take a match out of a box and strike it	Ability to perform an action
Do simple arithmetic	Ability to calculate numbers

When the hand and feet are weaker than the upper arms and legs, the problem is often a polyneuropathy—a disorder that affects all of the nerves outside of the brain and spinal cord (peripheral nerves). Polyneuropathies tend to affect the longest nerves first (those in the hands and feet). The person may have the most trouble with fine finger movements.

When weakness is limited to one side of the body, doctors suspect a disorder affecting one side of the brain, such as a stroke. Weakness that affects the body below a certain part may be caused by a spinal cord disorder. For example, an injury to the thoracic spine causes the legs but not the arms to be paralyzed. An injury in or above the neck causes paralysis of all four limbs.

Weakness may also occur in other patterns, such as those corresponding to one or more particular peripheral nerves. Strength may decrease with repetitive activity, as occurs in myasthenia gravis.

Sensory nerves carry information from the body to the brain about such things as touch, pain, heat, cold, vibration, the position of body parts, and the shape of objects. Abnormal sensations or reduced perception of sensations may indicate damage to a sensory nerve, the spinal cord, or certain parts of the brain. Information from specific areas on the body’s surface, called dermatomes (see art on page 796), is carried to a specific location (level) in the spinal cord, then to the brain. Thus, doctors may be able to pinpoint the specific level of damage to the spinal cord by identifying the areas where sensation is abnormal or lost.

The surface of the body is tested for loss of sensation. Usually, doctors concentrate on the area where the person feels numbness, tingling, or pain. A pin and a blunt object (such as the head of a safety pin) are used to see if the person can tell the difference between sharp and dull. Doctors also test the person’s ability to feel gentle touch, heat, and vibration. To test position sense, doctors move the person’s finger or toe up or down and ask the person to describe its position without looking.

Reflexes: A reflex is an automatic response to a stimulus. For example, the lower leg jerks when the tendon below the kneecap is gently tapped with a small rubber hammer. The pathway that a reflex follows (reflex arc) does not directly involve the brain. The pathway consists of the sensory nerve to the spinal cord, the nerve connections in the spinal cord, and the motor nerves back to the muscle. Doctors test reflexes to determine whether all parts of this pathway are functioning. The reflexes most commonly tested are the knee jerk and similar reflexes at the elbow and ankle.

The plantar reflex may help doctors diagnose abnormalities in the nerve pathways involved in the voluntary control of muscles. It is tested by firmly stroking the outer border of the sole of the foot with a key or other object that causes minor discomfort. Normally, the toes curl downward, except in infants aged 6 months or younger. Having the big toe go upward and the other toes spread out is a sign of an abnormality in the brain or spinal cord.

Testing other reflexes can provide important information. For example, doctors learn the extent of injury in a comatose person by noting whether the pupils constrict when light is shined on them (pupillary light reflex), whether the eyes blink when the cornea is touched (corneal reflex), and how the eyes move when the person’s head is turned or when water is flushed into the ear canal. Seeing the anus constrict when lightly touched (anal wink) is a good sign in a person with a spinal cord injury.

Coordination, Balance, and Gait: Coordination and walking (gait) require integration of signals from sensory and motor nerves by the brain and spinal cord. To test these abilities, doctors ask a person to walk in a straight line, placing one foot in front of the other. They ask the person to use the forefinger to reach out and touch the doctor’s finger, then the person’s own nose, and then to repeat these actions rapidly. The person may be asked to do these actions first with the eyes open, then with the eyes closed.

For the Romberg test, the person stands still with both feet together as close as possible without losing balance. Then the eyes are closed. If balance is lost, information about position from the legs is not reaching the brain, usually because the nerves or spinal cord is injured.

Reflex Arc: A No-Brainer

A reflex arc is the pathway that a nerve reflex, such as the knee jerk reflex, follows.

1. A tap on the knee stimulates sensory receptors, generating a nerve signal.

2. The signal travels along a nerve to the spinal cord.

3. In the spinal cord, the signal is transmitted from the sensory nerve to a motor nerve.

4. The motor nerve sends the signal back to a muscle in the thigh.

5. The muscle contracts, causing the lower leg to jerk upward. The entire reflex occurs without involving the brain.

Autonomic Nervous System: The autonomic (involuntary) nervous system regulates internal body processes that require no conscious effort, such as blood pressure, heart rate, breathing, and temperature regulation through sweating or shivering. An abnormality of this system may cause a fall in blood pressure when a person stands up (orthostatic hypotension), reduction or absence of sweating, or sexual problems such as difficulty initiating or maintaining an erection. Doctors may do a variety of tests, such as measuring blood pressure and heart rate while the person is lying down, sitting, and standing.

Blood Flow to the Brain: A severe narrowing of the arteries to the brain reduces blood flow and increases the risk of stroke. The risk is higher for people who are older, who smoke cigarettes, or who have high blood pressure, high cholesterol levels, diabetes, or disorders of the arteries or heart. Doctors place a stethoscope on the neck (over the carotid artery) and listen for turbulent blood flow through a narrowed or irregular artery (the sound of turbulent blow flow is called a bruit). However, the best way to diagnose disorders of the arteries is to use ultrasound (called carotid duplex and transcranial ultrasonography), magnetic resonance angiography (MRA), computed tomography angiography (CTA), or cerebral angiography. Blood pressure may be measured in both arms to check for blockages in the large arteries that branch off from the aorta. Such blockages sometimes result in stroke.

Procedures

Diagnostic procedures may be needed to confirm a diagnosis suggested by the medical history and physical examination. Imaging tests such as computed tomography (CT—see page 2037), magnetic resonance imaging (MRI—see page 2040), angiography (see page 2036), positron emission tomography (PET—see page 2044), and Doppler ultrasonography (see page 2044) are commonly used to diagnose neurologic disorders.

HOW IMAGING TESTS HELP IN DIAGNOSING NERVOUS SYSTEM DISORDERS

TEST	USES
Cerebral (catheter) angiography	To obtain detailed images of blood vessels of the brain
Computed tomography (CT)	To identify structural abnormalities (such as abscesses, tumors, and hydrocephalus) in the brain To identify bleeding or evidence of strokes in the brain To identify ruptured or herniated disks in the spine To identify spinal fractures To monitor the effects of radiation therapy on brain cancer or of antibiotics on a brain abscess
CT angiography (CTA)	To obtain detailed images of blood vessels of the brain (CTA has largely replaced cerebral angiography)
Doppler ultrasonography (carotid and transcranial)	To identify and evaluate narrowing or blockage of arteries in the neck and head and thus assess the risk of stroke
Magnetic resonance imaging (MRI)	To identify structural abnormalities (such as abscesses, tumors, and hydrocephalus) in the brain (images of brain tissue are clearer than those provided by CT, but MRI is not as readily available)
Magnetic resonance angiography (MRA)	To evaluate arteries in people who have had a stroke or TIA or in people who may have an aneurysm or arteriovenous malformation
Magnetic resonance venography (MRV)	To detect a blood clot in veins of the brain (cerebral venous thrombosis) and to monitor how treatment affects this disorder
Functional magnetic resonance imaging (fMRI)	To identify which areas of the brain are active when a task (such as reading, writing, remembering, calculating, or moving a limb) is done
Perfusion-weighted imaging (PWI) MRI	To estimate how much blood is flowing through a particular area of the brain
Diffusion-weighted imaging (DWI) MRI	To identify very early stroke and Creutzfeld-Jacob disease (CJD)
Magnetic resonance (MR) spectroscopy	To distinguish between abscesses and tumors
Positron emission tomography (PET)	To evaluate blood flow and metabolic activity in the brain To provide information about seizure disorders To help identify Alzheimer’s disease, Parkinson’s disease, transient ischemic attacks, and strokes

How a Spinal Tap Is Done

Cerebrospinal fluid flows through a channel (the subarachnoid space) between the middle and inner layers of tissue (meninges) that cover the brain and spinal cord—the subarachnoid space. To remove a sample of this fluid, a doctor inserts a small, hollow needle between two vertebrae in the lower spine, usually the third and fourth or the fourth and fifth lumbar vertebrae, below the point where the spinal cord ends. Usually, the person lies on the side with the knees curled to the chest. This position widens the space between the vertebrae, so that the doctor can avoid hitting the bones when the needle is inserted. Cerebrospinal fluid is allowed to drip into a test tube, and the sample is sent to a laboratory for examination.

Spinal Tap

Cerebrospinal fluid flows through a channel (the subarachnoid space) between the layers of tissue (meninges) that cover the brain and spinal cord. This fluid, which surrounds the brain and spinal cord, helps cushion them against sudden jarring and minor injury.

For a spinal tap (lumbar puncture), a sample of cerebrospinal fluid is withdrawn with a needle and sent to a laboratory for examination.

The cerebrospinal fluid is checked for evidence of infections, tumors, and bleeding in the brain and spinal cord. These disorders may change the content and appearance of the cerebrospinal fluid, which normally contains few red and white blood cells and is clear and colorless. For example, the following findings suggest certain disorders:

An increase in the number of white blood cells in the cerebrospinal fluid suggests an infection or inflammation of the brain and spinal cord.

Cloudy fluid, due to the presence of many white blood cells, suggests meningitis (infection and inflammation of the tissues covering the brain and spinal cord) or sometimes encephalitis (infection and inflammation of the brain).

High protein levels in the fluid may result from any injury of the brain, the spinal cord, or a spinal nerve root (the part of a spinal nerve next to the spinal cord).

Abnormal antibodies in the fluid suggest multiple sclerosis or an infection.

Low sugar (glucose) levels suggest meningitis or cancer.

Blood in the fluid may indicate a brain hemorrhage.

An increase in the fluid’s pressure can result from many disorders, including brain tumors and meningitis.

Before doing a spinal tap, doctors use an ophthalmoscope to examine the optic nerve (see art on page 1422), which bulges when the pressure within the skull is increased. If the pressure is increased because of a mass (such as a tumor or abscess), a spinal tap is not done because it may suddenly reduce pressure below the brain. As a result, the brain may shift and be pressed through one of the small natural openings in the relatively rigid tissues that separate the brain into compartments (called herniation—see art on page 735). Herniation puts pressure on the brain and is potentially fatal. The medical history and neurologic examination help doctors determine whether herniation is a risk. But CT or MRI of the head is usually more accurate and is often done as a precaution before a spinal tap is done.

For a spinal tap, people typically lie on their side and draw their knees to their chest. A local anesthetic is used to numb the insertion site. Then, a needle is inserted between two vertebrae in the lower spine below the end of the spinal cord.

During a spinal tap, doctors can measure the pressure within the skull. Pressure is measured by attaching a gauge (manometer) to the needle used for the spinal tap and noting the height of the cerebrospinal fluid in the gauge.

A spinal tap usually takes no more than 15 minutes and is usually done at the person’s bedside.

About 1 of 10 people develops a headache when standing up after a spinal tap. The headache usually disappears after a few days to weeks. Other problems are very rare.

Echoencephalography

Echoencephalography uses ultrasound waves to produce an image of the brain. This simple, painless, and relatively inexpensive procedure can be used in children younger than 2 years because their skull is thin enough for ultrasound waves to pass through. It can be done quickly at the bedside to detect hydrocephalus (commonly called water on the brain) or bleeding. CT and MRI have largely replaced echoencephalography because they produce much better images, especially in older children and adults.

Myelography

In myelography, x-rays of the spinal cord are taken after a radiopaque dye is injected into the cerebrospinal fluid via a spinal tap. Myelography has been largely replaced by MRI, which produces more detailed images, is simpler, and is safer. Myelography with CT is used when additional detail of the spinal canal and surrounding bone, which MRI cannot provide, is needed. Myelography with CT is also used when MRI is not available or cannot be done safely (for example, when a person has a heart pacemaker).

Electroencephalography

Electroencephalography (EEG) is a simple, painless procedure in which the brain’s electrical activity is recorded as wave patterns and printed on paper or recorded in a computer (see art on page 714). EEG can help identify seizure disorders, sleep disturbances, and certain metabolic or structural disorders of the brain. For example, EEG can identify where a seizure originates and show the characteristic electrical activity associated with confusion due to liver failure (liver encephalopathy).

For the procedure, an examiner places small, round adhesive sensors (electrodes) on the person’s scalp. The electrodes are connected by wires to a machine, which produces a record (tracing) of small changes in voltage detected by each electrode. These tracings constitute the electroencephalogram (the EEG).

If a seizure disorder is suspected but the initial EEG is normal, another EEG is done after using a tactic that makes seizure activity more likely. For example, the person may be deprived of sleep, be asked to breathe deeply and rapidly (hyperventilate), or be exposed to a flashing light (stroboscope).

Sometimes (for example, when a behavior that resembles a seizure is difficult to distinguish from a psychiatric disorder), the brain’s electrical activity is recorded for 24 hours or longer while the person is monitored in the hospital by a video camera. The camera detects the seizure-like behavior, and examination of the EEG at that moment reveals either seizure activity or continued normal electrical activity, indicating a psychiatric disorder. Video EEG is also used when preparing a person with epilepsy for surgery to see what type of seizure results from an abnormality in the particular brain area in which the seizure originates.

Evoked Responses

Stimuli for sight, sound, and touch are used to activate specific areas of the brain, that is, to evoke responses. Based on these responses, doctors can tell how well those areas of the brain are working. For example, a flashing light stimulates the retina of the eye, the optic nerve, and the nerve pathway to the back part of the brain where vision is perceived and interpreted. EEG is used to detect electrical activity evoked by the stimuli.

Evoked responses are particularly useful in testing how well the senses are functioning in infants and children. For example, doctors can test an infant’s hearing by checking for a response after a clicking sound is made at each ear. Evoked responses are also useful in identifying the effects of multiple sclerosis and other disorders on areas of the optic nerve, brain stem, and spinal cord. Such effects may or may not be detected by MRI.

Electromyography and Nerve Conduction Studies

Electromyography and nerve conduction studies help doctors determine whether muscle weakness, sensory loss, or both results from injury to the following:

Spinal nerve root (for example, due to a ruptured disk in the spine of the neck or lower back)

Peripheral nerve (for example, due to carpal tunnel syndrome or diabetic neuropathy)

Connection between nerve and muscle (neuromuscular junction), for example, due to myasthenia gravis, botulism, or diphtheria

Muscle (for example, due to polymyositis)

In electromyography (EMG), small needles are inserted into a muscle to record the electrical activity of the muscle when the muscle is at rest and when it is contracting. Normally, resting muscle produces no electrical activity. A slight contraction produces some electrical activity, which increases as the contraction increases. The EMG is abnormal if muscle weakness results from a problem with a spinal nerve root, peripheral nerve, muscle, or neuromuscular junction. The EMG produces a distinctive pattern of abnormalities. Unlike CT or EEG, which can be done routinely by technicians, EMG requires the expertise of a neurologist, who chooses the appropriate nerves and muscles to test and interprets the findings.

Nerve conduction studies measure the speed at which motor or sensory nerves conduct impulses. A small electrical current stimulates an impulse along the nerve being tested. The current may be delivered by several electrodes placed on the surface of the skin or by several needles inserted along the pathway of the nerve. The impulse moves along the nerve, eventually reaching the muscle and causing it to contract. By measuring the time the impulse takes to reach the muscle and the distance from the stimulating electrode or needle to the muscle, doctors can calculate the speed of nerve conduction. The nerve may be stimulated once or several times (to determine how well the neuromuscular junction is functioning). Results are abnormal only if the symptom results from a problem with a nerve or neuromuscular junction. For example,

Slow nerve conduction may result from a nerve disorder, such as carpal tunnel syndrome (painful compression of a nerve in the wrist).

If the muscle’s response is progressively weaker after repeated stimulation, a problem with the neuromuscular junction (as occurs in myasthenia gravis) may be the cause.

Disorders that affect only the brain, spinal cord, spinal nerve roots, or the muscle do not affect the speed of nerve conduction.