Medical mystery: The boy who couldn't get enough water

A 12-year-old boy came to his pediatrician because his family noticed that for weeks, he had been drinking about twice as much water as usual. Not surprisingly, he was constantly in the restroom, and had to wake up to urinate at least once every night.

He was previously healthy, was on no medicines, and had not lost any weight.  He said he had no headaches, abdominal pain, vomiting, nausea, diarrhea or painful urination.  His school performance remained strong, and he wasn't missing school other than needing to leave the classroom more frequently to go to the bathroom. He had minimal absences from school.

On examination, he seemed a little thin. His height was average, and his blood pressure was normal at 110/65.

Given the child's thirst and urination, the first thought was of diabetes mellitus (often known as "sugar diabetes") — specifically the autoimmune form of the disease, known as Type 1. The doctor asked the boy's mother if there was a family history of this or other autoimmune conditions such as hypothyroidism or celiac disease.  She said there was none.

The pediatrician also thought about Type 2 diabetes, which usually but not always is associated with obesity, darkening of the skin behind the neck (acanthosis nigricans), and a family history of Type 2. This seemed unlikely. though, given that the boy was thin and had no family history of the condition.

Nor did he have that telltale skin darkening, though he did have a bumpy rash near his groin and wrists.

His urine test was normal, with no evidence of sugar in the urine or infection, nor did it indicate that he was dehydrated. He had several blood glucose measurements as well as a Hemoglobin A1c (an indication of blood glucose levelsover the last 3 months).  Both were normal.

The boy was sent home, and his symptoms continued to get worse. After a few months, he was getting up as many as six times in the night to urinate. He was exhausted, and his grades in school were falling.

What was causing his symptoms?

Solution:

"Sugar diabetes" got its name because historically, patients' urine would be tasted to see if it was sweet, a sign of glucose in the urine. Fortunately, that job has been eliminated by blood glucose laboratory equipment. Still, the Greek name, diabetes mellitus, persists. "Diabetes" means to siphon (liquid is drawn out), and "mellitus" means "like honey."

While this condition was ruled out for this boy, what wasn't considered was a rare condition known as diabetes insipidus, from the Latin for "tasteless."

To understand what diabetes insipidus is, it is useful to review normal physiology.  If you were in the desert without much water, your body would make less urine, and make it more concentrated so minimal fluids are excreted.  Even overnight, the body conserves fluid this way, which explains why the urine is more concentrated on awakening than later in the day.

The kidneys concentrate the urine, but it is actually the brain which sends the command to the kidneys.  That message comes from the pituitary gland in the form of a hormone called vasopressin.  When the brain detects the onset of even mild dehydration, the pituitary releases vasopressin, which increases water reabsorption in the kidneys, making highly concentrated urine.

In diabetes insipidus, the body no longer can release vasopressin.  To diagnose this condition, the patient may have to go to the hospital and be deprived of fluids to see whether the urine concentrates normally. If not, there may be a lack of vasopressin.

Our patient had this study, confirming he had diabetes insipidus.  Giving him vasopressin resulted in his first well-concentrated urine — and a good night's sleep – finally,  after many months.

Pills and nasal sprays can effectively replace the missing vasopressin.  The endocrinologist's next job is to figure out what caused the pituitary gland to stop producing the vasopressin.

Some of the conditions which can cause diabetes insipidus include hypophysitis (inflammation of the pituitary gland), brain tumors, genetic conditions, and Langerhans cell histiocytosis (LCH). In LCH, there is an abnormal increase in white blood cells that can also lead to bony abnormalities and rashes.

In this case, the unusual rash in the groin and on the wrists were biopsied showing the abnormal cells of histiocytosis (LCH).  He was referred to the pediatric hematologic specialist to treat the LCH, and remains in the care of the endocrinologist to manage his diabetes.

Craig A. Alter, M.D., is Director of the Pituitary Center at the Division of Endocrinology and Diabetes at Children's Hospital of Philadelphia and a professor of clinical pediatrics at the University of Pennsylvania's Perelman School of Medicine.