On Wednesday I challenged readers to figure out the case of a middle-aged gardener with a fading rash, numbness and tingling and intermittent muscle contractions.

More than 400 readers weighed in with diagnoses that included pesticide poisoning, tick-borne disease, brown recluse spider bite, puss caterpillar toxin, scorpion sting, foxglove intoxication, sporotrichosis (a fungal infection sometimes called “rose gardener’s disease”), tetanus and a severe allergic reaction to his plastic gardening shoes.

And the winning diagnosis is…Black widow spider bite.

The first reader to figure this out was Sally from Chicago, who wrote:

Is this a case of a black widow spider bite? I’m not sure if that diagnostically fits with the crazy day-glo rash (in fact, I can’t think of anything that does!), but I guess that could be consistent with vascular spread of venom. The rest of the symptoms fit right in with lactrodetism: the absence of obvious bite site, the limited rash, the spreading myalgia and numbness/tingling, the overall flulike symptoms and, most significantly, the spasms. Makes me feel like I’m back in the third grade and calling all the spiders I see black widows, but who knows!

How the Diagnosis Was Made:

Dr. Tress Goodwin, the emergency room doctor who saw the stricken gardener, recognized early on that his illness was probably due to some kind of venom, though it wasn’t clear where the toxin may have been injected. There were no puncture marks, so a snake bite was unlikely. Bee and ant stings can cause bodywide symptoms, but these symptoms usually progress rapidly, and the local reaction is usually quite dramatic.

Arachnids — spiders, ticks and scorpions — often poison their prey with fast-acting toxins. And while most of these toxins are not deadly to humans, they will cause some local pain and sometimes more widespread symptoms. There are scorpions along the East Coast, and though their stings can be quite painful, they rarely cause symptoms beyond the area where the toxin was injected.

Spiders are a far more common cause of serious injury. Two in particular can cause serious illness: the brown recluse spider, which usually causes a severe lesion at the site of the bite, and the black widow spider, which can cause local symptoms but can also cause more widespread illness. Caterpillars and centipedes can also cause toxic envenomations.

Dr. Goodwin couldn’t be sure what this patient was suffering from and decided to simply treat his symptoms and keep an eye on him. She treated the muscle contractions with Ativan, an anxiety-reducing drug that helps the body to relax. She also gave him Benadryl, just in case this was an allergic reaction to a sting or bite. Finally, she gave him a tetanus shot, because any time you have a possible break in the skin outdoors there is an opportunity for infection by clostridium tetani, the bacteria the causes tetanus.

After several hours the muscle contractions became less frequent, and the patient was sent home with instruction to follow up with his regular doctor and to return if symptoms worsened. The muscle contractions disappeared by the next day, but he felt tired for a good two weeks afterward.

Seeking an Expert’s Advice:

Dr. Goodwin remained puzzled by the case and wrote to one of her teachers from medical school, an expert in envenomations.

From: “Tress Goodwin”

Sent: Monday, August 23, 2010 10:18:19 AM

Subject: Interesting case from Stanford SOM Alum

To: Robert L Norris Hi Dr. Norris- I know you are the envenomation guru and wondering if you had a chance to look at this case. We discharged him, so nothing urgent. We are just curious. I am attaching the images that he took at home. 37 y/o M no PMH, working in garden about 4 hours PTA felt numbness in right lower leg, looked down and noticed a rash. NO pain. Rash was patch like, almost fluorescent in color on the anterior aspect of shin and ankle and on thigh. He described it as if “you took a glow stick from Halloween and poured it on my leg.” Soon after noticed numbness and tingling traveling from toes to mid thigh, as well as numbness/tingling in right hand and right jaw. Also reported diffuse muscle contractions about q 15 minutes lasting 10-15 seconds with associated “dizziness” and nausea. No known bite marks, no snake at the scene. Unclear if there were spiders or any other venomous creatures. Here in the ED his exam was normal — normal neuro, sensory. His skin exam here was not as “violacious” as the attached image — more of a flat macular lacy rash with no pain, non-petechial. Again NO pain. He still was having spasms and nausea. We gave him ativan and benadryl here with IVF and he felt better–watched him for 5 hours. There was no indication to admit, so we discharged. Any insight would be helpful! Thank you,

Tress Goodwin

Her teacher wrote back:

Tress, Interesting case… I would, indeed, suspect some form of envenomation. The skin coloration is a bit odd, but given the rapidity w/ which it appeared, I’d assume some form of nonspecific reactive dermatitis — possibly direct histamine release (local, therefore likely not IgE-mediated). I assume he had no subsequent necrosis. Given the paramount sxs of muscle spasms and nausea, I’d suspect a widow spider bite/Latrodectus evenomation. Bite itself can go unnoticed. Was there any evidence of diaphoresis? Could you find any evidence of a puncture wound? I think your course of care was very appropriate – I’m sure you documented his tetanus status. Best wishes, Bob Robert L. Norris, MD, FACEP, FAAEM

Professor of Surgery

Chief, Division of Emergency Medicine

Stanford University Editor-in-Chief

Wilderness and Environmental Medicine

Her reply:

From: Tress Goodwin

Sent: Tue, Aug 24, 2010 at 1:00 PM

Subject: Re: Interesting case from Stanford SOM Alum

To: Robert L Norris Thank you so much for your response! To answer the questions — no significant necrosis, he was initially diaphoretic but not in the ED. We didn’t note any puncture wounds and did update his tetanus. I will let him know — he should probably wear pants the next time he gardens! Thank you again and hope all is well out on the farm. I miss it there. Tress Goodwin

Dr. Goodwin forwarded the e-mail to her patient, who tells me that he has, in fact, made it a point to wear long pants and closed shoes while working in his garden.

The Deadliest Spider:

Black widow spider bites cause more deaths worldwide than any other spider, in part because they are among the most wide-ranging toxic spiders on the planet. Although their venom is powerful, they rarely inject enough of it to kill a human. In fact, there have been no deaths from black widows in the United States for over a decade.

The venom travels through the bloodstream and has its greatest effect on nerve cells and the cells that produce adrenaline. The nerves are overstimulated and so cause a persistent sensation of pins and needles and muscle cramps. Unlike most spider bites, the black widow bite causes no pain and little local inflammation. Many who are bitten, like this man, realize that they have encountered the spider only after symptoms appear. There is an anti-venom medication available to treat the poison from the bite, but severe reactions to the drug are common, so it is used only when the black widow venom causes life-threatening illness.

So, this man’s illness was caused by a black widow spider bite — probably. The setting, the symptoms, the course and timing of events are consistent with that diagnosis. And of all the creepy, crawly creatures considered by the doctors involved in the case (and then by you, Well readers), the black widow spider is the most common. On the other hand, no spider was seen scuttling away. No bite marks were found. There is no test for black widow spider venom. So this was a clinical diagnosis — one made on the basis of the data collected from the patient and his exam. One made without a smoking gun. This is how most diagnoses are made in medicine. We don’t catch the criminal red-handed. We figure out what is probably true and work from there. Because, often enough, that’s all we’ve got.