Differential diagnosis has nothing to do with the back end of a car but everything to do with getting satisfaction from your doctors. Once you’ve followed your Yellow Brick Road to the specialist’s office, it’s tempting to trust the pearls of wisdom rolling from the mouth of the medical wizard. Just take your medicine like a munchkin and dance your way through the rest of your life.
If you dare to question the diagnosis, you might, in the case of mysterious ailments, like polymyalgia rheumatica or fibromyalgia, be granted a short explanation of how the wizard has excluded all other possibilities by means of a sophisticated tool called “differential diagnosis”, a thing no mere mortal should attempt.
On your handy tablet, which of course you have sneaked into the sanctum santorum in your purse or back pocket, you discover that Wikipedia says,
“There are various methods of performing a differential diagnostic procedure, but in general, it is based on the idea that one begins by considering the most common diagnosis first: a head cold versus meningitis, for example. As a reminder, medical students are taught the Occam’s razor adage, “When you hear hoofbeats, look for horses, not zebras,” which means look for the simplest, most common explanation first. Only after ruling out the simplest diagnosis should the clinician consider more complex or exotic diagnoses.”
Hmmm. Have you told the specialist about the zebras in your life? Wikipedia tells you what to expect from your wizard:
“Differential diagnosis has four steps. The physician: [sic]
- Gathers all information about the patient and creates a symptoms list. The list can be in writing or in the physician’s head, as long as they [sic] make a list.
- Lists all possible causes (candidate conditions) for the symptoms. Again, this can be in writing or in the physician’s head but it must be done.
- Prioritizes the list by placing the most urgently dangerous possible causes at the top of the list.
- Rules out or treats possible causes, beginning with the most urgently dangerous condition and working down the list. Rule out—practically—means use tests and other scientific methods to determine that a candidate condition has a clinically negligible probability of being the cause.
Well, that sounds reasonable, although you may be forgiven for wondering what is really listed inside the wizard’s head or what constitutes “tests and other scientific methods”. If the wizard’s diagnosis is, “You’re fine—go home and sleep it off” or some fancy Latin words that seem like blarney, you may opt to rip aside the curtain to the side of the wizard’s visage—
–and there stand four surprised creatures in strange, awkward-looking clothes, who introduce themselves as siblings, with a nervous glance in the wizard’s direction, as if about to give away the keys to the kingdom to a mere serf. “I’m Vindicatem the Mnemonic,” says the eldest looking. “Doctors most often rely on me to advise on the order in which they should consider multiple possible pathologies:
The next two creatures snigger. “That’s because you’re simple!” titters one. “And never passed statistics!” chimes in the other. Obviously twins, they are dressed in black-and-white motley, like a cross between a clown and a math text. “Call me Epidemiology,” suggests the first.
“Skip Eppy,” insists the other. “I’m faster and more natural and reliable. Call me Likelihood Ratio—Likely for short.”
You point to a tyke in a tutu who’s pedaling madly on a trike around the legs of the others. “Who’s that?”
“WHOIFPI,” all three chorus, stopping the grinning tyke in its tracks. “Stands for Would Have Occurred in the First Place in the Individual,” explains Likely. “Eppy’s sidekick.”
“Very handy whenever we’re attacked by those darned computer programs,” growls Eppy.
“Speaking of which,” breaks in WHOIFPI, pedaling maniacally offstage, “to the barricades!”
Unintelligible screeches like, “Essajill! Illyad! Cue-em-are! Jezabell!” fill the air as winged computer discs bash against the barred windows and door.
Had enough of state-of-the-art differential diagnosis, a.k.a. DD? Fling the curtain across and click your heels together.
So, after fifteen weeks of carrying around a diagnosis of polymyalgia rheumatica and little else, have I been truly DDed?
I presented in the ER one afternoon as a female Caucasian in her sixties with sudden onset of pain and stiffness particularly in the shoulder and pelvic girdles, fatigue, CRP of 80 (normal is 1 or 2), low red blood cells, low ferritin, low hematocrit. History of colon cancer, fibromyalgia, nonfunctional thyroid, miscarriage, galactorrhea. An electrocardiogram came out normal, which ruled out Giant Cell Arteritis.
The diagnostic criteria (for research) thus far established by the European League against Rheumatism (EULAR) and the American College of Rheumatology (ACR)—the same people who established fibromyalgia criteria ‘way back in 1990—for PMR include three required and four additional criteria. Required are (1) age over fifty, (2) both shoulders aching and (3) abnormal CRP or ESR. The other four are (1) morning stiffness longer than 45 minutes, (2) hip pain, (3) no rheumatoid factor and (4) no peripheral joint pain, worth 2, 1, 2 and 1 point respectively. If you score four or more on those last points as well as having the first three requirements, you may be a PMRry.
Bullseye! I scored three plus five. No wonder the doc in the hospital looked so satisfied with his diagnosis and waved a prednisone prescription at me. No wonder, on that busy day, that the low iron, the outrageous CRP (inflammation marker), and the (noticeably endocrine) history were ignored.
But that’s just for research purposes. Before differential diagnosis. Once it is established that another disease explaining the findings is not present, the clinical diagnosis can be made if the patient (1) is fifty or older at onset, (2) suffers aching and morning stiffness on both sides longer than half an hour for more than two weeks and involving two or all of (a) the neck or torso, (b) shoulders and arms, or (c) hips and thighs, (3) has an ESR (sedimentation rate) higher than 40 mm/h and (4) swiftly responds to low-dose prednisone.
Are we there yet? Not in my book. My ESR has not been measured (I was told that at least in BC you get either the CRP or the ESR, but not both). I haven’t taken prednisone. And won’t, which means that, technically, I will never be a PMRry.
After fifteen weeks, differential diagnosis has barely begun. From the articles on PMR Dr. T gave me, I learned that the following diseases need to be excluded before that clinical diagnosis can be made:
- rheumatoid arthritis
- Remitting Seronegative Symmetrical Synovitis with Pitting Edema, a.k.a. puffy edematous hand syndrome
- multifocal local musculoskeletal disease
- bone diseases: multiple myeloma, hyperparathyroidism, or osteomalacia
- drug-induced myalgias or myositis
- inflammatory myopathy: polymyositis or dermatomyositis
- infective endocarditis
- Lyme disease
- malignancy: rheumatological manifestations of myelodysplastic syndromes
- vasculitis other than Giant Cell Arteritis (renal involvement)
- crowned-dens syndrome (soft-tissue calcifications)
Other materials suggest that PMR might be caused by chlamydia pneumoniae or mycoplasma pneumoniae, or hyperthyroidism, or may be affected by low DHEA or low sulfur.
Of that long list, thus far only rheumatoid arthritis, fibromyalgia, endocarditis, depression, and drug-induced stuff have been knocked off the list. Parkinson’s and local musculoskeletal disease are unlikely. DHEA was tested and came out normal. Cortisol was tested but results are out of whack. I filled my sulfur insufficiency with MSM, which fixed the knee synovitis. The stiffness in the shoulder and pelvic girdles has been reduced, possibly as a result of faithfully following a stringent protocol of organic food and nutraceuticals, but who knows? The red-blood-cell count and hematocrit remain under par and the CRP is higher than ever.
Some of the ten or twelve diseases on that DD list are far scarier than PMR, which is said to disappear by itself, often, after two years or so. But what if so called PMR could be a temporary manifestation of a far more serious disease process, which goes unremarked?
Meanwhile, new symptoms have turned up: hands so stiff I can’t make a fist or lay them flat, terrifying nerve pain from the tips of the right-hand middle fingers to the spine, pathetic day-long muscle weakness, forty pounds of weight loss and counting, and a continual longing to go back to bed, as much as fifteen hours per day.
Some of the tests that could knock off more items from the DD list involve endocrine organs, which fits with my own hunch that endocrine disruption has something to do with this mess. To my medically unschooled mind, my physical history points in that direction. When one considers the level of stress in our society, its effect on the adrenals and thus on the endocrine system, and the plethora of people sick with mysterious “auto-immune disorders”, is it really so crazy for a patient to inquire after the state of those endocrine organs? To insist on differential diagnosis being carried out instead of being satisfied with “having” a disease whose origins are unknown?
Apparently. The specialist’s office just informed me I don’t need another appointment for my fibromyalgia [sic] since everything possible has been done for me.
Until I cave and take prednisone, I suppose.
At least in my case, those critters behind the curtain are not exactly working their tails off.