New-Onset Foot Drop in a Patient with Low Back Pain: Screening Before the Plan of Care
A 58-year-old man is referred to outpatient physical therapy with a 3-week history of right low back pain radiating into the lateral calf. He reports that over the past 5 days his right foot has begun to 'slap' when walking and he has tripped twice. He has hypertension and type 2 diabetes (HbA1c 8.9%), takes metformin and lisinopril, and denies bowel or bladder change. On observation he ambulates with a steppage pattern on the right. Strength: right ankle dorsiflexion 3/5, right great toe extension 2/5, right ankle plantarflexion 5/5, left lower extremity 5/5 throughout. Sensation is diminished over the right dorsal foot and lateral calf but intact over the medial malleolus and sole. Right ankle reflex is absent; left is 1+. Straight leg raise reproduces radiating pain at 40 degrees on the right. The referral requests 'lumbar stabilization and modalities.'
1. Identify the findings that do not fit a simple L5 radiculopathy and explain why they matter for differential diagnosis and urgency.
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The distribution and pattern point to a common fibular (peroneal) neuropathy at the fibular head rather than, or in addition to, an L5 root lesion:
- Sensation: diminished over the dorsal foot and lateral calf but spared over the medial malleolus and sole. The medial malleolus/saphenous territory is L4, and the sole (medial/lateral plantar) is S1 - sparing of these does not by itself separate L5 from common fibular. The more discriminating clue is that the entire common fibular distribution (deep and superficial) is involved while the tibial-innervated plantarflexors remain 5/5. An L5 root lesion can do this too, so the exam alone is not decisive - but a lesion that is purely common fibular with no L5 sensory loss in the L5-only territory favors nerve entrapment.
- Reflex: an absent ankle reflex is not typical of L5 (that is S1); its absence here is more consistent with the coexisting diabetic peripheral neuropathy suggested by the HbA1c of 8.9%, which confounds the picture.
- The key urgency point: acute, progressive, painless or minimally painful foot drop with weakness of both dorsiflexion and toe extension, especially with a slapping gait and falls, must be screened for cauda equina / conus medullaris compression and for a focal compressive or ischemic mononeuropathy. He has no saddle anesthesia or bladder/bowel change, which is reassuring, but the deficit is progressive over 5 days and he is falling. Progressive motor deficit is a red flag that warrants same-day communication with the referring provider rather than proceeding with a stabilization program.
Document the red-flag screen (saddle sensation, bladder/bowel function, bilateral symptoms, perineal sensory change) explicitly, and communicate the progression and fall risk the same day.
2. The referring provider is unavailable and the patient asks to 'just start therapy today.' State your immediate management decision and justify it using the examination findings.
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Do not initiate a conventional lumbar stabilization and modality program today as the primary plan. Instead:
- Escalate: contact the referring provider (or covering provider) the same day with a structured report: progressive 5-day foot drop, 3/5 dorsiflexion, 2/5 great toe extension, two falls, absent right ankle reflex, HbA1c 8.9%. Request urgent evaluation for the progressive motor deficit.
- Safety and function now: the patient is falling. Provide immediate fall-prevention education and an assistive device (e.g., a single-point cane or, given the steppage pattern, consider an AFO referral/evaluation), home safety instruction, and clear return precautions (worsening weakness, new numbness in the saddle region, any bladder/bowel change → emergency care).
- Why not 'just start': the deficit is progressing, and the differential includes a compressive radiculopathy, a fibular neuropathy, and - less likely but catastrophic if missed - cauda equina syndrome. Beginning an exercise program without addressing the progression risks harm and delays definitive care. Modalities would not address a progressive motor deficit.
- What you can legitimately do: gait training with the device, ankle dorsiflexion strengthening within a safe, monitored program is reasonable only after the provider has been notified and the plan is coordinated - and even then it does not substitute for medical evaluation of a progressive deficit.
The judgment the exam is testing: progressive neurologic deficit + falls = escalate and protect, not treat-and-see.
3. Assuming the workup ultimately confirms an L5 radiculopathy without surgical indication, outline the prognostic factors and the elements you would include in the plan of care.
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Favorable prognostic indicators: motor deficits from radiculopathy often improve over weeks to months with conservative care; younger age, shorter symptom duration, absence of progressive deficit, and preserved plantarflexion all favor recovery. Unfavorable/limiting factors here: diabetes with poor glycemic control (slower nerve recovery, coexisting peripheral neuropathy), age, and fall risk.
Plan of care elements:
- Impairment level: progressive resisted ankle dorsiflexion and great toe extension; neural mobilization as tolerated; address the diabetic neuropathy contribution through glycemic counseling and referral to the care team.
- Activity/function: gait training with emphasis on foot clearance; trial and fitting of an AFO if dorsiflexion strength does not recover enough to prevent trips; balance and fall-prevention training; home exercise program.
- Monitoring: re-measure MMT and sensation each visit; track falls; define objective discharge criteria (e.g., dorsiflexion ≥4/5, no falls in 4 weeks, independent community ambulation).
- Coordination: communicate with the endocrinology/primary care team about glycemic control; re-refer to the physician if weakness progresses or new red flags appear.
- Education: prognosis, expected timeline, activity modification, and warning signs.