A family-medicine doctor recent saw a 13-year-old with a weird, unidentifiable rash. It wasn't itchy or painful, and the teenage boy hadn't traveled anywhere recently. So the the doctor did what any modern physician would do: he took a photo and uploaded it to an Instagram-style app called Figure 1.

"13 y/o M with rash on his knee for 2 months," the doctor with the username inder70 wrote. "it is not itchy, no pain, no travel, no new food no inciting agent, no medications?"

The suggestions came piling in. One doctor asked if it was fungal ("no itchiness or raised border," inder70 responded). Most of them quickly landed on the same diagnosis: granuloma annulare, a skin condition that has no known cause and can be treated with certain ointments. "Thanks everyone!!" inder70 responded, the medical mystery solved.

Hospital hallway conversations, gone digital

Figure 1 is the brainchild of Josh Landy, an internist from Toronto. He did his residency at Stanford and saw constant, off-the-cuff consults happening in hospital hallways, where doctors would try and talk through the details of a case that was surprising or new to them.

"It can be 4 a.m. when you're working, and you're going to see something that can astonish you," Landy said. "It might be the most classic textbook example of something you don't know about, and it happens when there are not a lot of other people around. So the idea was there has to be a better way to communicate."

Landy started doing research on his fellow residents and found that 13 percent were already using their smart phones to share images with one another via email or text message. What if there was a wider network to share those images and get more input from not just one hospital's residents, but the wider medical community?

"it can be 4 a.m. when you're working and you can see something that astonishes you"

That's where Figure 1 comes in: since its launch in the spring of 2013, the app has accrued 115,000 users. It's most popular, unsurprisingly, among young doctors: an estimated 20 percent of medical residents now have Figure 1 on their phones. There are sections on dermatology (lots of rashes), radiology (mostly x-rays), and emergency medicine (not for the faint of heart).

Not all of these users are doctors: Landy estimates that about 10 percent of the users are non-health care professionals (people like me, which explains how I was able to see that image and discussion above). Only doctors, however, can comment on cases — and they do, a lot.

Some of the doctors are sharing images they find interesting: "Kitchen knife vs. thumb. Pretty minor but I've never seen someone stitch through a nail like this!" one doctor wrote under a photo that, as you can imagine, is a thumbnail with stitches. But a lot of the app is doctors seeking advice and asking other professionals to give their opinions on cases.

For example, a radiologist recently asked others to look at an x-ray of an elderly woman who "fell backward onto the floor." A registered nurse posted a photo of the phlegm her patient had coughed up ("Any idea what this may be??"); another shared a photo of a patient's urine that elicited a 77-comment chain discussing the diagnosis.

Privacy, diagnosis issues raised

One of the persistent questions about an app like Figure 1 is privacy. Few patients would want their faces to turn up in the public forum. Landy said the approach to protecting privacy is twofold: doctors are required to ask permission to take a photograph, and they can't capture any identifying details. That explains why you see a lot of limbs on Figure 1, but no faces.

The issue I was interested was whether Figure 1 raised issues of liability. If another user suggested a diagnosis — and the doctor posting the photo followed through — could that put the commenting user at potential fault for something going wrong? It's easy to see a patient, in the future, going back to Figure 1 to trace the comment thread that may have contributed to her treatment.

Landy said this wasn't an issue that had come up much yet in Figure 1's short lifetime and that these interactions were arguably just another version of the corridor consults that already happen. "These are people who are talking about a lot of the cases because they're interesting, textbook, classic versions and they can help," he said.