A Discourse on Zebras

Greetings, gentle reader. Dr. Cranky regrets to report, once again, that he has neglected to refill his psychotropic medications. As a consequence, the only way your faithful scrivener can stop the voices in his head is to take to his keyboard in an attempt to exorcise the inner demons which torment his very soul. So let us venture into those dank, dismal and untidy recesses of the Cranky mind and see what we can find lurking about in the dark. Abraham Lincoln once spoke about “the better angels of our nature.” Then again, President Lincoln never met Dr. Cranky.

“My goodness Dr. Cranky,” you might think to yourself, “You have certainly chosen an odd subject for today’s disquisition. What on earth do zebras have to do with medicine?” Alas, dear reader, these equine mammals represent nothing less than a Herculean task for practitioners of the medical arts. At some point all budding young Aesculapians must come to grips with how, or even if, they will try to pursue them. Do you see the picture above? Those zebras are laughing at you, and with good reason.

The reluctance to pursue zebras usually begins when a group of medical students find themselves rounding with their Attending physician whilst on an inpatient service. At some point the Attending will ask one of the students what diagnoses should be considered given a specific constellation of signs and symptoms. The student, hoping to impress his elder, will mention one or two rare conditions as part of his differential diagnosis. This is the signal for the accompanying Residents and Interns to smirk and smile at each other while the Attending, in the most paternalistic and condescending way possible, wags his finger at the student and quips “when one hears hoof beats he should think of horses and not zebras.” The ostensible purpose of this exercise is to demonstrate to the student that rare diagnoses (i.e. zebras) are unlikely and should only be considered infrequently in medical practice. More likely than not there is a secondary intent to this exercise as well: such aphorisms allow the Attending, Residents and Interns to demonstrate intellectual superiority over their unwashed underlings in the most public and embarrassing way they can.

The reason Dr. Cranky has been thinking about zebras is because of a conversation he recently had with a colleague. Your earnest host had just made an unusual diagnosis and Dr. Y, one of his partners, inquired “tell me Dr. Cranky, how is it you keep finding all these unlikely diseases?” The question was a reasonable one. In the prior 8 months your faithful scribe had made the following diagnoses, each of which could be thought of as rare or uncommon. All are lethal or horribly debilitating if not diagnosed early:

  • Two separate cases of spinal epidural abscesses (estimated incidencerate of 0.2 to 2.8 cases per 10,000 population per year).
  • One case of Boerhaave syndrome (A 1980 review by Kish cited only 300 cases in the literature worldwide).
  • One case of cauda equina syndrome in the setting of spinal stenosis (estimated incidence rate of 2.72 cases per 10,000 population per year).

At the time, and given the hectic pace of the Emergency Department that day, the best answer Dr. Cranky could give his inquisitive partner was “I guess it’s because I look for them.” Later, after he had an opportunity to think about this conversation, he realized he must have sounded like a pompous ass. Please do not misunderstand. Your dutiful scribe was not filled with hubris. He does not think of himself like this:

And humble, too. Don't forget humble!

Dr. Cranky has a much more realistic opinion of himself. At times he can barely write his name in the ground with a stick. Here is an actual copy of his medical school graduation portrait:

Dr. Cranky at his very best

Nevertheless, the question did set your humble servant to thinking about the process of how physicians make their diagnoses and how medical training and cultural inculcation do their best to interfere with it. Let us examine one of the above patients, whom we shall call Mr. A, and look at those factors which gave Dr. Cranky an intimation that something out of the ordinary was afoot.

Mr. A presented on a Sunday afternoon, which is typically a busy and hectic time for most Emergency Departments across this great land of ours. Dr. Cranky picked up the chart and read his latest patient’s Chief Complaint as being “fever of one week’s duration.” A quick glance at the vital signs revealed his temperature to be 99.2 F, blood pressure 133/79, pulse 89, respiratory rate 14 and oxygen saturation 99% on room air. Mr. A had a past history of Type 1 diabetes mellitus and hypertension. He claimed good compliance with his medications. His initial blood glucose, which was obtained at the triage desk, was 260. At this point Dr. Cranky did not have much information available to construct a differential diagnosis, but did recall that Type 1 diabetics are notorious for being immunocompromised and thus at risk for serious infectious complications.

Your host then made his way to room 30, where Mr. A had taken up temporary residence. Whenever Dr. Cranky walks into a patient’s room he always thinks of the Big C and his sage advice. “The first thing you should do,” he admonished, “is to take in the entire scene and develop a gestalt or overall impression. In most cases a good emergency physician will know, using observation alone and within just a few minutes, whether or not a patient is seriously ill.” Upon entry, Dr. Cranky observed his patient to be about 35 years old and laying quietly on the stretcher with his eyes closed. He was well-groomed and appeared to be of middle to upper-middle class socioeconomic status. His wife sat next to him and was dressed well but conservatively. Mr. A opened his eyes and smiled, but the facial features surrounding his eyes belied genuine discomfort. His voice was well-measured and lacking in any local accent. His grammar and vocabulary were well-informed. From this information your faithful servant was able to discern that Mr. A was an educated and responsible individual, most likely compliant with his medication and dietary regimen, and not prone to exaggerating his complaints. In fact, Dr. Cranky needed to be extra cautious since such people are well-known to be stoic and minimize their symptoms.

“Good afternoon Mr. A., I’m Dr. Cranky and I’ll be taking care of you,” your tireless author stated. “What brings you to visit with us today?”

“I think I’m having trouble with my diabetes,” Mr A began. “I usually have good control of my blood sugar but over the past week they’ve been elevated and difficult to control.”

Your thoughtful scribe noted that his patient did not begin with the chief complaint as stated in the chart. As an educated individual, there was a good chance that Mr. A had researched his diabetes and knew that fever associated with loss of glycemic control was worrisome.

“Is there anything else,” Dr. Cranky inquired.

“No, not really.”

“Now John, that’s not so,” Mrs. A interjected. “Tell the doctor about your fever and your foot.” With this interruption Dr. Cranky found confirmation of his suspicion that Mr. A was the sort of individual who tended to discount his symptoms. This also told your host that he might need to be more direct than usual in his questioning.

“Well,” the patient said, “for the last week I’ve had this sore on the top of my foot and a slight fever.”

“That’s not quite right,” the wife amended, “Your foot hurts so much you haven’t been able to walk since last night. I took your temperature myself this morning and it was 103. And don’t forget how you were drenched in sweat and started shaking just before we came here. You said you felt so cold.”

“Have you had any recent respiratory infections, cough, sore throat, stuffy nose, abdominal pain or urinary tract symptoms,” Dr. Cranky asked?


It was now that Dr. Cranky knew, based on history and observation alone, there was a strong chance his patient was seriously ill. The accompanying symptoms of diaphoresis (excessive sweating), rigors (involuntary trembling) and chills supported this concern. One possible source of his fever was the presence of a diabetic foot, whereby infection can spread rapidly through the fascial planes of this part of the lower extremity. Osteomyelitis, an infection of the bones of the foot, might also occur. Diabetic ketoacidosis (DKA), in which the body’s control of glucose metabolism breaks down, was an additional concern although unlikely since Mr. A’s respiratory rate was only 14. Visual inspection revealed no evidence of Kussmaul’s respirations (deep and fast breathing) which are usually associated with the acidemia found in DKA.

“Is there anything else,” Dr. Cranky asked again?

“I was here about five days ago and saw Dr. M. She drew some blood and gave me a prescription for an antibiotic. Oh yeah, I almost forgot. I’ve had this pain in the back of my neck as well.”

“Have you ever had pain in your neck before?”

“Yes, I have a history of spinal stenosis and chronic neck pain. Sometimes my arms go numb.”

Dr. Cranky decided to keep this last bit of information in the back of his mind for the time being. His examination of Mr. A was completely unremarkable with two exceptions. The first abnormality was found on examination of the right foot. The sole of the foot, where diabetic complications usually occur, was pristine. There was a shallow ulcer on the top, however, with a small amount of purulent drainage but no surrounding cellulitis, induration or abscess to suggest an extension of the infection. This was worrisome because such a superficial wound would not be expected to produce such intense symptoms. The second finding was a decrease in Mr. A. upper extremity strength from the shoulders down. When Dr. Cranky asked the patient to squeeze his fingers, he noticed a slight grimace of the face.

“Are you usually weak like this?”

“I guess so.”

“Does it usually hurt when you grip something?”


Your host outlined his course of action for Mr. A and his wife. The nurse would come in and start an IV. Blood would be sent for a CBC since an elevated white cell count would support the presence of a serious infection. A comprehensive metabolic profile and serum acetone would be examined to assess for DKA. A chest x-ray and urinalysis would be obtained for look for other sources of fever. Wound and blood cultures would be drawn to determine the presence of bacteremia (bacteria in the bloodstream). An x-ray of the foot was ordered to screen for osteomyelits.

Dr. Cranky then went to his computer and looked up Mr. A’s visit from earlier in the week. Dr. M had performed a similar workup and everything appeared to be negative. She had appropriately started the patient on Augmentin, an antibiotic commonly used to treat diabetic foot ulcers and told Mr. A to follow up with his primary care physician within two days for reevaluation. It was then that Dr. Cranky noticed the red font highlighting the previous visit’s wound and blood cultures. Whenever there is an abnormal laboratory result the computer’s software changes the letters of the test name from blue to bright red. Dr. M would not have had access to these results since it can take several days for a culture to become positive. Your dutiful scribe double-clicked on the crimson font and what he saw made his blood suddenly run cold. The wound culture, as well as both blood cultures, were positive for MRSA!

And just what is MRSA, you might ask? The letters M-R-S-A are an acronym for Methacillin-Resistant Staphylococcus Aureus, a particularly nasty bacteria resistant to numerous antibiotics. It is thought to have resulted from antibiotic overuse by the medical community during the past several decades. The lay press, with their usual penchant for sensationalism, have dubbed this organism the “flesh-eating bacteria.” However, for certain strains of the bug this is not mere hyperbole. And Mr. A had this nasty and aggressive bacteria growing in his blood.

It is at this point where the decision to chase after a possible zebra comes into play. Up to this point, the story of Mr. A is typical for what emergency physicians deal with every day. It would not be unreasonable to start such a patient on an antibiotic which covers for MRSA, such as Vancomycin, admit him to the internal medicine service and move on to the next patient. But your faithful servant’s brain is not wired that way. As Mrs. Cranky (who is not at all cranky herself) would say, he tends to be a “worry-wart.” And Dr. Cranky was very worried. Something bad was possibly happening to his patient and he immediately went back to room 30 to speak with Mr. A again.

“Tell me more about your neck pain,” he asked.


“I said, tell me more about your neck pain.”

“Well, it started last Tuesday. The day before I came here and saw Dr. M.”

Your host could feel a queasy sensation start in the pit of his stomach as his Spidey-sense began to tingle.

“When was the last time your neck hurt before then?”

“What does this have to do with my fever,” Mr. A asked. He could see the worry on Dr. Cranky’s face.

“Probably nothing, but tell me. When was the last time your neck hurt before last Tuesday?”

“I don’t know. Maybe five or ten years ago.”

The tingle rose another couple of notches. It had been a long time since Mr. A had experienced neck discomfort so there was a possibility his pain was not just from his spinal stenosis.

“And your arms. Do they feel numb.”

“I guess so.”

Mr. A was continuing to be evasive. Although he does not like to do so, Dr. Cranky felt the need to be more direct and started asking his patient leading questions.

“Would it be reasonable to say your arms are more numb than usual?”

“Possibly. What’s this all about?”

Your host ignored his patient’s question and persisted. “Would you say it’s possible that your arms are more weak and numb than they have ever been before?”

“Well, yes. As a matter of fact, they are.”

The needle on Dr. Cranky’s Spidey Sense-O-Meter jumped up to 11. Suddenly it all came together. The increased neck pain, associated with worsening arm numbness and weakness suggested the possibility of spinal cord compression. Yes, it was possible that these symptoms were simply a recurrence of his long-standing cervical stenosis. However, Mr. A didn’t usually have neck pain. He also complained of chills, rigors and fever. These symptoms pointed to the presence of a serious infection but there wasn’t an apparent source and his superficial foot ulcer wasn’t extensive enough to fit the bill. And last, but most importantly, Dr. Cranky’s patient had MRSA growing in his blood. The worst-case scenario in such a situation would be the presence of a dreaded spinal epidural abscess.

“This is all well and good,” you might say, “but tell us, Dr. Cranky, what is a spinal epidural abscess and how does one get such a thing?” Your host applauds such an inquisitive nature. Let us pause from our story for a moment and consider some basic pathophysiology. First of all, consider the normal anatomy of the spinal canal.

An illustration from Dr. Cranky's Guide to What Things Look Like Inside your Spine

As you can see, there is a fibrous sheath which surrounds the spinal cord. This is called the dura. There is a space between this covering and the vertebrae which is called the epidural space. The Latin prefix epi– means “above, over or covering.” Hence, the epidural space is that space which can be found above the dura. An epidural abscess is a collection of bacteria and pus which is located within this space. Doctors worry about such a thing for two reasons:

  1. Infection is bad.
  2. Anything which pushes on the spinal cord is bad.

Infection is bad because bacteria like to eat body structures which perform important functions and dump toxic metabolic waste into their immediate environment. Spinal cord compression is bad because neural tissue has all the firmness and consistency of warm jello and is easily injured.

“That’s all quite interesting Dr. Cranky,” you might say, “but how does one come to be in possession of such a pathological process?” Again, your host is glad you asked. One possible source comes from an infection which starts at a remote site, such as the skin, where bacteria tend to hang out while fulfilling their bacterial purpose in life. The body has a whole host of defenses at this potential “portal of entry” which keep such purveyors of disease at bay. So long as the body’s defenses are adequate, all is well. However, if a species of bacteria is especially aggressive (such as MRSA) and/or a person has a weakened immune system (such as with diabetics) then it is possible for these organisms to get into the blood stream.

As previously mentioned, the presence of bacteria in the vascular space is referred to as bacteremia. The Latin suffix -emia refers to the presence of something in the blood. Normally, any foreign organisms which find their way into the bloodstream are quickly destroyed by the body’s immune cells. In some cases, such as with Mr. A, they survive long enough to take an exit ramp off the vascular superhighway and set up residence in some body part such as the intervebral disk (that light blue thing in the diagram above). This infection, referred to as discitis, may extend to include the vertebral body. Once enough white blood cells have accumulated as part of the body’s attempt kill off the offending organisms an abscess is said to develop. This is a surgical emergency and such a collection of infected material needs to be drained as soon as possible.

An MRI of what Dr. Cranky is talking about

Let us now get back to the story of the taciturn Mr. A. With such pathological worries as these running around loose in his head Dr. Cranky immediately asked the patient’s nurse, who just happened to be the ever-resourceful Sweet Sandra, to expedite repeat blood cultures and start Vancomycin immediately. Next, your stout yeoman ordered an MRI of his patient’s cervical and thoracic spine to determine if the dreaded epidural abscess was indeed present. Dr. Cranky knew what would happen next and prepared himself for a possible argument.

“Dr. Cranky, it’s the MRI tech,” the clerk called out soon after he had written the order. “They want to know if you’ve asked the radiologist for permission to get the MRI on Mr. A.” This was not an unusual occurrence for a Sunday afternoon. Although the ED where Dr. Cranky works sees a volume of approximately 85,000 patients a year, the MRI scanner is not scheduled to operate on the sabbath day. Permission had to be sought from the radiologist, who was located somewhere deep within the bowels of BCMC, before things could proceed further. “Not yet,” Dr. Cranky replied, “Pray, please inquire of this scurrilous knave the identity of that person from whom we need to seek authorization and call them forthwith.” And so it was done.

“Dr. D is on the phone for you,” the clerk declared fifteen minutes later. Dr. Cranky breathed a sigh of relief. He had worked with Dr. D on many occasions over the past several years and knew him well. It is a curious phenomenon that younger (and less experienced) radiologists tend to regard their tech’s pursuit of leisure time to be of the utmost importance and some have been know to decline permission in situations such as this. Dr. D, however, was an older and trusted compatriot and your earnest scribe knew he would listen to reason.

“Hi George,” Dr. Cranky said as he picked up the phone. “I think I might have another spinal epidural abscess on my hands.”

“You’ve go to be kidding,” Dr. D retorted, “you just had one two months ago.” Dr. D’s response was not unexpected. A spinal abscess is a rare find for any emergency department and two cases just a few months apart would be most unusual. “Are you sure you’re not on some zebra hunt here?” Dr. Cranky quickly summarized the story of Mr. A. along with the reasons for his concern.

“I’ll call in the tech,” Dr. D said without pause.

The labs came back and it started to look like your faithful servant might have indeed gone “on safari.” The WBC was only slightly elevated at 11.5 and there was no left shift. From the rest of the workup Dr. Cranky could tell that Mr. A was not in DKA and was not suffering from pneumonia, a urinary tract infection or osteomyelitis. It was then that Dr. D called back.

“What’s the story, George,” Dr. Cranky inquired with some apprehensiveness.

“Mr. A. has discitis at C6-7 with an epidural abscess extending from T1 up to C4. You know this uses up your lifetime quota for this diagnosis, don’t you Cranky?”

“It’s a pleasure doing business with you, George. I’ll call the neurosurgeons and send Mr. A downtown so they can heal with some cold steel.”

“Anytime,” Dr. D said as he hung up the phone.

And so it was that Mr. A found himself going downtown to BCMC where he met with some very nice neurosurgeons. As nice, that is, as it’s possible for neurosurgeons to be. He underwent a decompressive laminectomy later that day, the bad humors were released from his spinal canal, and he ended up doing quite well. And yes, the cultures from his abscess were positive for MRSA.

So what can we learn about hunting zebras from this tale of the stoic Mr A? Quite a bit, actually. But unfortunately, dear reader, these lessons will have to wait for another day. The voices in Dr. Cranky’s head are now just a mere whisper and your favorite physician must rest.

Fret not, and don’t forget that good things come to those who wait.

About Dr. Cranky

Dr. Cranky is a residency-trained, board-certified emergency physician who has been fighting in the trenches of American medicine for far too long. Each day he tries to stay one step ahead of burnout. Despite his best efforts, burnout seems to be closing in fast.
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