We’ve all been taught that when you hear hoofbeats suspect a horse. But what about when you hear a lot of hoofbeats? Couldn’t one of them be a zebra?? Possibly even a unicorn???
Because I see a lot of patients with back pain. Are they all horses? This week’s med student case of the week is brought to you by Hannah Duane.
Patient is a 60’s y.o. man with a h/o chronic low back pain that he relates to years of factory work presenting for evaluation of flank paint that radiates down his leg. He reported that 2 days prior to arrival he developed some left lower abdominal wall numbness and flank pain that radiates around to the front of the abdomen after he administered an insulin shot. He then developed thigh numbness as well as a sense of weakness of the leg. Today he started developing weakness of the right leg which precipitated evaluation.
So. Weakness bilaterally. Likely not a stroke. We’re given a history of back pain so naturally we should be asking about other caudal equina symptoms. Really, ask (and document) a caudal review of systems to every patient you ever see with back pain.
He reports no saddle anesthesia. Urination is unchanged from baseline (he has a history of prostate cancer with a prostatic seed implant) but is having no retention or incontinence. He did have trouble having a bowel movement this morning.
Remember, that initially the bladder retains urine, the incontinence is an overflow issue that develops after retention, so clarify with patients that they can fully empty their bladder. And note the cancer history, certainly spinal mets just got added to the differential.
He has normal vitals. Abdominal exam is unremarkable. He has good rectal tone. Neuro exam documents that he has decreased sensation to the left medial thigh and 4/5 hip flexion strength on that side.
So, a couple points. First, if he has significant weakness he’s going to need advanced imaging. Second there’s a benign condition fairly common in diabetics known as meralgia paresthetica where inflammation or compression of the lateral cutaneous nerve of the thigh causes lateral thigh paresthesias. That nerve has no motor component however; any motor findings rule that out. We then want to ask whether we are worried about an upper or a lower motor nerve problem, this is the time to do a good reflex exam, as well as proprioception, vibratory, and cold sensation. (Kill two birds with one stone by putting your tuning fork in an ice bath so you can use it for back-to-back tests). Unfortunately for our purposes the results of these weren’t documented.
Labs were mostly unremarkable with a WBC count of 4, a glucose of 252, and a recent HgbA1c documented as 9. The patient had a CT scan initially (I believe there was going to be significant delay in getting MRI).
CT scan shows DISH (Diffuse Idiopathic Skeletal Hyperostosis – you can see all the fusion of the thoracic vertebrae) as well as some lumbar posterior osteophytes. He underwent an MRI as well:
While there is certainly some narrowing there, it wasn’t felt to significantly impact the cord and so the patient was not thought to benefit from surgery. He underwent spinal tap with PCR looking for various viral causes of transverse myelitis, these were negative as well. Ultimately he improved spontaneously; neurology consultation suspected a form of insulin-related neuritis. I was not familiar with this, per Up-to-date apparently it is a small fiber neuropathy occurring in patients with chronic hyperglycemia who have a decrease in HgbA1c of more than 2 points over 3 months (whether using insulin or oral agents). (So not only are we supposed to go slow in fixing the blood sugar of DKA patients, we’re supposed to go slow with non-DKA patients too).
Takehomes? First, neurology is hard. Second, there may have been further physical exam findings that may have made us less surprised that the MRI wasn’t positive – not that they would have kept you from doing it though. Third, while this patient didn’t end up having discitis or epidural abscess, any provider seeing patients with back pain is going to end up seeing these conditions eventually, always keep it in your differential!
Feldman EL et al. Epidemiology and classification of diabetic neuropathy. Up-to-date (last updated Dec 15, 2016, lit review current through Oct 2017). Accessed 2 Nov 2017.