Duncan is unkempt, his hair greasy. His voice is monotone, with minimal facial expression, also called a flat affect. On top of our scratch paper, I write: "depressed?" But that's not why his parents brought him in.

Since I'm a doctor, when I tell people that I wrote a book, they usually say, "oh, that's terrific, like, a textbook?" (assuredly relieved I won't ask them to buy it.) But, then I tell them, "no, actually, it's a mystery. It's called Little Black Lies, about a psychiatrist searching for the truth about her mother's death." Most people are a bit intrigued (or at least polite enough to humor me), and the question comes up. A neurologist writing a mystery — how does that happen?

Truthfully, the leap from neurologist to novelist isn't all that extreme.

As a doctor, I write stories all day. I see patients, distilling their lives into consults in a language rich with Latin and colorful syndromes. Patients are protagonists in their own novels, and with each patient visit, I write another chapter. They get married, divorced, have babies, switch gender, lose a hundred pounds, lives full of plot twists, romance, and intrigue. But, patients don't just come by to chat, they come for help. As soon as they step into the exam room, they are asking me to solve their problems – which makes me a mystery writer too.

Let me explain. Join me, for a day in the life of a neurologist.

It's 8:15 A.M. and we open our first chart.

The "chief complaint" (what brings the patient in) is written in capital letters at the top. "FALLING." Sometimes a chief complaint gives the whole story away, "head-ache," for instance, or "seizure." But falling is pretty vague – could be anything from Parkinson's disease to a sprained ankle. We knock on the door to see "Duncan," a sixteen-year-old male, on the examining table, anxious parents besides him.

Where do we begin? The first rule of seeing patients is: observe. How does our patient speak and move? How does he dress? In our case, Duncan is unkempt, his hair greasy. His voice is monotone, with minimal facial expression, also called a flat affect. On top of our scratch paper, we write: "depressed?"

But that's not why his parents brought him in. FALLING.

Now it's time for the story. Our chart may be thick with details, backstories and plot points: MRIs, CTs, EEGs, EKGs, EMGs and other acronyms a-plenty. But none of this matters without the patient's history, his story. We go with the usual opener. "How are you doing today?"

"I'm fine," he grumbles, not even looking up. "My parents are crazy."

Not an auspicious start, but we push on. "I understand you've been falling?"

"A little. Sometimes. It's not a big deal."

With supreme effort, we drag out the story that he fell a couple of times in gym, "when he and his friends were doing a prank." His parents say it's happening more than that. At first they thought it was a clumsy teenager thing. But the last time, Duncan was on the floor for ten minutes, completely unable to move.

"When did that happen?"

"Right after he stood up for his trumpet solo," the father answers.

Was he dizzy? Light-headed? Did he pass out?

No, no, and no. Duncan is very clear on this account. He "wilted" to the ground. He was not light-headed and didn't faint, the way he did once after his blood was drawn. This particular time, he could hear everything: the school nurse, the EMTs, but he still couldn't move. We add to the scratch pad: "seizure?"

"And," the mother adds, "he's been really tired."

New complaint. Falling and tired. "Is that so? How tired?"

"A little," Duncan admits.

The father steps in here. "Not just a little. He's falling asleep everywhere."

We probe further and find that the father is not exaggerating. Duncan falls asleep on the school bus, through his classes, at the dinner table, and even once while playing trumpet at band practice. He fell asleep at a heavy metal concert. He's not just a little tired, he's half-asleep.

"He's also having," the mother clears her throat, "hallucinations. We think."

Duncan reluctantly tells us about "shadows watching him and holding him down" when he falls asleep. Once he saw spiders dangling from the bedroom fan and tried to swipe them away, but he couldn't move. Oh, and one more thing, he's been getting head-aches lately. We scribble in "head-aches."

Next step: the physical exam. Performed and completely normal. We are now ready to pronounce the diagnosis, drum-roll please, when Duncan turns beet-red, and says, "oh, and my nipples have been kind of sweaty."

Wait a second, hold that. Let's rewind. Sweaty nipples?

We had just finished our jig-saw puzzle, and now we have one piece left with too many tabs. What do we do now? Let's take it step-by-step.

We have sleepiness, hallucinations, and falling. Slam-dunk diagnosis: narcolepsy with cataplexy. How did we get that? This degree of sleepiness is the hallmark of narcolepsy. Hallucinations (hypnagogic, or upon falling asleep, or hypnopompic, upon waking up – don't you love Latin?) are also common in narcolepsy, often paired with sleep paralysis, the sensation of being fully paralyzed while awake.

Then there's the reason Duncan came to see us in the first place, falling. But not just falling any old time, only in emotional situations. With laughter, or anxiety, such as playing a trumpet solo. Weakness in an emotional situation is called cataplexy. Remember those videos you saw in high school, of the dogs running to get their food then keeling right over? You got it, cataplectic dogs. And what could be more exciting than chow-time?

Narcolepsy with cataplexy is a fairly common disease, about 1/2000, the same rate as MS, and it often presents in teen-age years. No one really knows the cause, it's thought to be auto-immune, where the body fights against itself for unknown reasons, similar to diabetes or hypothyroidism. So we have our diagnosis, but what about those head-aches? And even more, what about those sweaty nipples?

Plot twist! We need to put our thinking caps back on. This mystery is not over. Duncan has narcolepsy with cataplexy. But, that's not all. He has secondary narcolepsy with cataplexy, meaning something else is causing it. In this case, the salient clue being his sweaty nipples. We suspect he may have a benign brain tumor.

Where did we come up with this one?

Well, Duncan is right, and he is wrong. His nipples are not sweating, they are lactating or producing milk, also known as galactorrhea. Yes, it is possible for a man to produce milk. Unusual, but not impossible. If the body is producing the wrong hormones and turning on the lactation glands, this can occur. Which is exactly what happens with an active pituitary adenoma, a benign tumor in the middle of the brain sending the pituitary gland into overdrive. Which can also, by the way, cause narcolepsy with cataplexy.

We do an MRI of the brain, and confirm it. Surgery is scheduled, tumor removed, and Duncan is cured. And, I get to write about that too.

As a writer, I love a good mystery. But as a doctor, I love a happy ending even more.

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