Do I Have Parkinson’s? Article 2: Differential Diagnosis and the Neurologist

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As was discussed in the 1st article of this three-part series, neurologists who face a patient with possible Parkinson’s have no definitive test: no scans, no blood tests or spinal taps with which to base their diagnosis. Parkinson’s disease is what is referred to as a “clinical diagnosis.” This means that the decision as to whether or not a patient truly has Parkinson’s requires an extensive face to face interaction with a neurologist. That meeting usually involves a thorough history-taking or interview, and a comprehensive physical examination. Although very often videotaping or other aids are used, the diagnosis totally depends on the clinical acumen of the neurologist as he/she investigates what the patient presents in word and on exam.

To sum up the approach very briefly, while interviewing and examining the patient, the neurologist creates a running list of possibilities in his/her head. This list is called the “differential diagnosis,” often referred to a just the “differential.” A good neurologist much like a good detective, keeps adjusting, refining the differential as if it were a list of suspects. He/she redirects the line of questioning and the focus of the physical exam based on ruling in and ruling out suspects.

Each of the findings helps the neurologist to continuously reshuffle and re-prioritize the differential. As the list narrows to just a few possibilities, he/she will ask further questions and refine the examination. Then the patient is sent for tests that might rule out other possibilities. For instance, patients get a brain CT or MRI not to diagnose Parkinson’s but to rule out larger structural causes that might mimic Parkinson’s symptoms like a brain tumor or even multiple sclerosis. Often an electrical stimulation and measurement of nerve response in an affected limb called an EMG (electromyogram) is done to rule out local nerve injury as another cause.

If everything points to Parkinson’s the patient is given a trial of a drug that either replaces or mimics dopamine. If the patient shows improvement then everyone can be pretty certain it’s Parkinson’s

The point is that there is no single protocol or textbook pathway to making the diagnosis. Though the neurologist follows a formal structure to cover all the so-called bases, the specifics of that path highly depend upon the findings along the way, which guide each next step within that structure.

Early Parkinson’s can be difficult to diagnose because it presents differently in every patient, and often with symptoms that can easily be dismissed as minor like a small persistent twitching, sleepiness, a minor tremor, and even depression or anxiety attacks.

A typical story everyone has either experienced or heard of is that one or two of the ten common early warning symptoms (Part 1) show up and on that first visit to a neurologist the twitching pinky finger (in Michael J. Fox’s case) or in my own, new-onset depression, either get dismissed or symptomatically treated. I was given an antidepressant and when a tremor developed it was dismissed as a side effect of the antidepressant. It was not until I was completely unable to play piano and had inordinate difficulty writing, both from severe slowing in my right hand, that I was then fully worked up.

In either case, mine or Mr. Fox’s, nobody made a mistake or missed anything important. It’s just that for instance any one or two of the ten warning signs can be interpreted as due to other causes, and usually is.

Review of early symptoms:

  1. Tremor or shaking greater on one side
  2. Small handwriting
  3. Loss of smell
  4. Trouble sleeping
  5. Trouble/stiffness in moving or walking
  6. Constipation
  7. Soft or Low Voice
  8. Loss of facial expression, “masked facies”
  9. Dizziness and fainting
  10. Stooping or hunching over

I have added two more to this list:

  1. EDS (excessive daytime sleepiness) or fatigue
  2. New-onset psychiatric disorder (usually depression or anxiety attacks)

Once PD is suspected, a host of other diseases and conditions need to be considered and ruled out. That’s where the so called “differential diagnosis” list comes in. Each differential list is slightly different depending on what the patient presents to the neurologist and in admiration to neurology as a specialty, these lists can initially be quite large. Ruling out all the other causes on the list before PD reaches the top requires a solid working knowledge of each list item and how it is diagnosed.

Other lab tests and scans are used to rule out other causes but ultimately, Parkinson’s disease is a clinical diagnosis with the most essential “test” being that first old-fashioned face to face discussion with, and physical exam by a seasoned neurologist.

Example:

A 42 year old woman, a cello player in the local symphony, presents to the neurologist complaining of tremor in her right hand and difficulty manipulating the bow while playing. Sadly she has been politely asked to “take a break” from her job with the symphony until she gets adequately evaluated. She has also become quite depressed over the incident. She says the tremor actually goes away when she’s playing but it feels like the bow is “caught on something” and so she cannot sweep it across the strings as swiftly.

Here’s a sample starting differential diagnosis for someone presenting with a persistent tremor of the right hand. Although the fact that the tremor occurs at rest and goes away with movement, and especially combined with the fact that it occurs only on the right side elevates PD to #1 on the list.

Sample differential diagnosis list for Parkinson’s (remember that the neurologist must have extensive working knowledge of how each of these presents):

  1. Parkinson’s Disease
  2. Essential tremor (a nonspecific tremor of unknown cause and which does not get worse)
  3. Brain Tumor: she will have to have a CT scan or MRI scan of the brain
  4. Damage to the nerves in the arm in the affected side by trauma or multiple sclerosis(MS). She will likely undergo EMG nerve evaluation of the right arm.
  5. Other degenerative neurologic diseases, a long sub-list, details of which I shall skip:
    • Benign familial tremor
    • Dominant SCA (Spinal Cerebellar ataxia)
    • Cerebellar ataxia
    • Olivopontocerebellar degeneration
    • Familial Basal ganglion calcification (Fahr’s syndrome)
    • Alzheimer’s syndrome
    • Amyotrophic lateral sclerosis
    • Dementia, Lewy-body type
    • Parkinsonism-dementia complex
    • Progressive supranuclear palsy
    • Cerebellar degeneration, subacute
    • Shy-Drager syndrome
    • Striatonigral degeneration
    • Corticobasal Degeneration syndromes
    • Frontotemporal dementia
  6. Lesions of the basal ganglia where the brain controls movement by stroke/hemorrhage
  7. Lyme disease
  8. Drugs (her primary doctor put her on nortriptyline for depression)
    • Antipsychotic medications
    • Antidepressants
    • Lithium
    • Amphetamines
    • Cocaine
    • MPTP (a byproduct of bad practices in making Ecstasy that can induce a parkinson’s like syndrome after a single dose)
  9. Alcohol or narcotic withdrawal
  10. Alcoholic brain degeneration

After performing a directed interview and examination, her neurologist utilized his own fund of knowledge and experience, and did not think she showed features of any of the other degenerative diseases listed.

On physical exam and observation he noticed that she would swing her right arm less when walking down the hallway. She even slightly dragged her right foot.

He had her copy some sentences out of a medical text. It took her a long time and the writing was very small.

When he held her arm and moved it at the wrist and elbow he could feel a ratcheting rather than smooth passive movement (known as “cogwheeling”, a classic PD sign).

She denied any drug history and rarely consumes alcohol.

She’s from San Diego where Lyme-carrying deer ticks don’t flourish.

An MRI scan of her brain was normal so there’s no brain tumor or evidence or stroke/hemorrhage, and no defects suggestive of MS. Parkinson’s generally yields a very normal brain scan. Some research techniques that use radioactive dopamine-like compounds can reveal a defect however they are not generally available, and unnecessary as we see here that the diagnosis can be adequately made without it.

Her EMG nerve exam showed normal nerve function in the affected arm.

Finally, and extremely important in establishing Parkinson’s as her diagnosis, he placed her on a drug that mimics dopamine and examined her a week later. She showed almost none of the previous findings on that second visit after a week on the drug.

At that point the neurologist was certain it was PD and gently broke the news to her.