Musings of a Dinosaur

A Family Doctor in solo private practice; I may be going the way of the dinosaur, but I'm not dead yet.

Friday, February 01, 2008

Clinical Case: Leg Pain (Part 1)

Here is another in my occasional series (ok, it's only the second) designed to illustrate specific teaching points in Primary Care. As before, this is most definitely NOT the typical case presentation of some bizarre diagnosis intended to show off how smart I am. In fact, my intent is to highlight an error in my thought process with the hope that others might learn and avoid the same pitfall in their own clinical practices. (Unless I was just really stupid and no one else would ever make the same kind of mistake I did.) I have received the patient's full and explicit permission to post this case.

A 60-year-old white female smoker came to my office complaining of right leg pain for five years. it was described as a tightness in the front of the thigh that came on after walking five blocks or less. When she stopped to rest, the pain abated promptly within one minute. Over time she had noticed it gradually increasing in severity. There was no complaint of any pain or discomfort in the left thigh, either lower leg or foot. She was taking Lipitor for an elevated LDL (224 in 1997; on statins since then.) She was on no other medications and had no other medical problems.

On examination, her blood pressure and BMI were within normal limits. The right leg was unremarkable. There was no swelling, tenderness, deformity or asymmetry of color or temperature. I thought her right pedal pulses were somewhat diminished compared to those in the left foot. The rest of her general physical examination was completely normal.

My diagnosis was claudication; pain caused by a blockage in the flow of blood to the right leg that only produced pain when extra blood flow was needed -- as with walking. As soon as she stopped and the muscle's need for extra blood flow decreased, the pain went away. Although the classic location for intermittent claudication is the calf, I felt the patient's description and timing of the pain -- along with her status as a smoker -- made it the most likely diagnosis.

The simplest, cheapest and least invasive test to document problems with blood flow to the legs is pulse volume recordings performed with doppler ultrasound. Here was the report:
Normal amplitude of the arterial curve, a normal contour of the curve and a normal systolic pressure with an [ankle brachial index] of 1.0 on the right and 0.98 on the left. This study is essentially normal, with no evidence of vascular occlusive disease involving either lower extremity.
With a report showing normal blood flow to both legs, I began thinking about other causes of leg pain with exercise that abates with rest. There's something called spinal stenosis, a narrowing of the spinal canal that exerts pressure on the spinal cord with an upright posture. Bending forward relieves the pressure and the pain. I called the patient and asked again about how her pain was relieved; does she typically bend over when she takes a rest from walking? She wasn't sure; she thought she usually sat down. It was easy to visualize someone hunching over while seated, so I thought, "Close enough." I got an MRI of her lumbar spine which showed focal right-sided paracentral disk protrusion at T12L1, but no stenosis or cord compression. The patient then requested an x-ray of her right hip, thinking the pain might be from arthritis. The films were normal.

Next, she saw an orthopedic surgeon who felt the MRI abnormalities had nothing to do with the pain. He felt it was neurogenic, started her on Lyrica and referred her to a neurologist.

The neurologist ordered another study which confirmed the correct diagnosis.

Post guesses in the comments. I expect that many, if not most, will be correct. I'll put the answer up in a few days. Remember, this is not an exercise in diagnostic obscurity. It is an example of an erroneous thought process interfering with a simple diagnosis.

17 Comments:

At Fri Feb 01, 08:21:00 PM, Blogger Evan said...

Meralgia?

 
At Fri Feb 01, 10:55:00 PM, Blogger frizzzzle said...

Statins cause muscle pain as a possible side effect, don't they? I'll use that as my guess. Sorta odd it would only affect one leg, but my medical knowledge is awfully limited.

 
At Fri Feb 01, 11:35:00 PM, Anonymous Anonymous said...

meralgia paresthetica.

 
At Sat Feb 02, 05:00:00 AM, Blogger The MSILF said...

Why not something mechanical? Muscle strain/sprain?

Though the first thought was spinal stenosis too.

 
At Sat Feb 02, 08:01:00 AM, Blogger #1 Dinosaur said...

Nope to all of the above.

I went back and added three words to the post to try and avoid being too misleading.

Feel free to try again.

 
At Sat Feb 02, 10:57:00 AM, Blogger frylime said...

only an M1, so my little black book of diseases is quite limited...

myasthenia gravis? it just popped into my head...probably too "intense" to be this diagnosis though...

 
At Sat Feb 02, 01:08:00 PM, Blogger MedStudentGod (MSG) said...

I *still* think it sounds like claudication (maybe of the profunda femoris?), but I'll post guesses towards patellofemoral syndrome or iliotibial band syndrome.

 
At Sat Feb 02, 11:33:00 PM, Blogger Midwife with a Knife said...

Hm... polymyalgia rheumatica? Not quite a classic presentation... but.... she fits the demographics, kind of.

 
At Sun Feb 03, 04:36:00 PM, Anonymous Anonymous said...

lateral femoral cutaneous nerve syndrome

 
At Sun Feb 03, 09:39:00 PM, Blogger TBTAM said...

I'm thinking that maybe the heels on her shoes are worn unevenly and she is increasingly pronating. Maybe she just needs new heels.

 
At Mon Feb 04, 12:55:00 AM, Blogger Candace said...

I think it's either knee OA with referred pain to the thigh

OR

It's diabetes, undiagnosed with a femoral neuropathy.

But I'm an internist. So, you know my hammer now.

 
At Mon Feb 04, 09:44:00 AM, Blogger William the Coroner said...

I vote for knee OA. Though my patients never complain about a missed diagnosis.

 
At Mon Feb 04, 04:36:00 PM, Anonymous Anonymous said...

Femoral hernia.

 
At Mon Feb 04, 05:29:00 PM, Blogger Artemis said...

I'm probably making this too difficult, but here goes: Meralgia paresthetica is typically made worse with sitting, not activity, so I don't think that's correct (normal BMI also goes against this diagnosis). The MRI report suggests a small disc bulge which is too high for root compression typical of central canal stenosis and does not abut the nerve root at that level - I agree with the orthopedist that this isn't likely the cause of her symptoms. Pain has been present for 5 years but only with exertion. She's been on statins for 10 years, which are known to lead to muscle pain and cramping, but usually in a symmetric distribution. Nonetheless, I'd d/c the Lipitor and see what happens...EMG would exclude other myopathies, but without weakness or abnormal reflexes I don't think that's what she's got. I do wonder if your diagnosis of claudication was correct in the first place, but that the test you ordered wasn't sensitive enough to find a focal lesion; arteriography of the right leg might provide the information needed to confirm the diagnosis.

I'll be thinking about this for a while, wondering what I failed to read in your write up...
A

 
At Tue Feb 05, 10:15:00 AM, Anonymous Abby Normal said...

Her purse would smack her leg as she walked?

 
At Tue Feb 05, 02:45:00 PM, Anonymous Surfie said...

Low potassium -- something metabolic. The last study demonstrated it, but you didn't say what type of study it was. I'm assuming it was blood work as that hadn't been done yet (or at least that you said).

 
At Mon Feb 11, 11:12:00 PM, Anonymous Anonymous said...

If i had to guess of the bat I think its something common:

patellar tendonitis?

but then you said the neurologist ordered a study...

meaning its probably something involving nerves...

-sounds like a possible nerve root compression

-possibly some other radiculopathy?

-transverse myelitis?

-MS even...

 

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