Why we should never ask if your saddle-region is numb

I guess the ideal doctor would have experienced first hand every condition that can affect a human. He or she would then be able to pattern recognise what the patient is describing, and tease out the relevant information during history taking to diagnose the problem.

The ideal doctor is not possible, so we instead rely on reading textbooks, reviews and listening to clinical pearls from experienced colleagues. We also gain experience over time.

The common theme to all of these sources is that ultimately the information comes from patients. Patients are our ultimate clinical tutor for history taking.

This is what makes this podcast on back pain especially brilliant. You have the uniquely useful situation where the patient is the doctor, describing his own case.

I listened to this podcast during my car journeys, and one point stuck with me. When the doctor-patient was asked “Do you have numbness around your buttocks?” he would always answer no. When instead he was asked “Does it feel different when you sit down?” he would answer yes. He found it difficult to explain exactly how it was different, but it just felt funny.

He ended up having cauda equina.

So, with this in mind here’s the case. A 65-year-old man had a background of chronic back pain. Whilst bending over to do some gardening, he had a sudden onset of pain in his lumbar back.

The pain was central and 10/10 severity. It worsened with sudden movements, coughing and weight bearing. It was relieved by lying flat. The pain stopped him sleeping, and was progressively worsening. There was radiation to the right leg only. There was some tingling in the left leg. He was finding it harder to walk, and he was normally an independently mobile man.

A red flag review revealed:

Fracture risk:

No known osteoporosis
Osteoporosis risk factors: maternal hip fracture
No major or minor trauma

Malignancy risk:

PMH of melanomas, surgically excised 5 years ago
No weight loss
Some night sweats for the past week with fever for the past two days
No thoracic pain
No point tenderness
Age > 50

Infection risk:

No immunosuppression
Fevers and night sweats as noted
Age > 50

Neurological involvement, including CE:

“Does it feel different when you sit down?”
“Yes”
“How so?”
“It feels like I’m always sitting on a pillow.”

“Any changes to your bowel habits?”
“I haven’t gone in the past two days.”
“And does it feel different in any way when you wipe yourself?”
“Yes – it’s numb.”

No bladder symptoms
No weakness
Some new paraesthesia in the left foot

On examination

There was diffuse erythema and warmth around the L3/L4 area. No point tenderness, but tender to palpation diffusely from L1-L5 ish. The pain was worst centrally, and there was no paraspinal tenderness or obvious muscle spasm.

Straight leg raise caused pain at 5 degrees elevation, with pain spreading all the way down the leg into the feet as well as pain in the back. This was bilateral. Ankle dorsiflexion worsened the pain, again bilaterally.

Neurologically, power was intact. All lower limb reflexes were normal, with downgoing plantar reflexes. Sensation was abnormal perianally. The patient described it as lots of layers of cloth between the skin and the stimulus.

I organised an urgent MRI and referred to orthopaedics. I’ll post tomorrow what the outcome of all this was.

The case bore striking resemblance to the podcast’s story, of ‘different’ but not numb perianal sensation. On a BMJ article on cauda equina, it gives a patient’s perspective which reinforces this further:

“…I remember wiping myself with the toilet paper and it feeling decidedly odd—not completely numb but distant. It was my refusal to admit to numbness that fooled my general practitioner. He asked if I could feel him touching me, not whether his touch felt normal…”

I guess the lesson from this post is: don’t just ask for the presence or absence of sensation. Ask the patient to describe if the sensation is different in any way. This goes not just for cauda equina, but history taking and examination for sensation in general.