Introduction
This patient’s pathway to diagnosis and treatment was carried out by multiple clinicians within the team. The initial telephone consultation was conducted remotely. After this telephone consultation, it was decided that a face-to-face appointment was required for a full neurological assessment. The case was then discussed together, and pathways agreed.
Presenting Problem
Initial Phone Assessment:
A 51-year-old female participated in an initial remote assessment for FCP clinic.
Subjective:
- In October 2022, the patient underwent gastric band surgery and has since lost 7 stone.
- In February 2023, she began experiencing frequent tripping with her right foot and noted complete numbness in the anterior shin, the top of the foot, and the toes.
- She is unable to actively lift her toes on the right foot but retains normal sensation under the foot and can scrunch her toes.
- To compensate, she walks with exaggerated knee flex to clear her foot from the floor.
- There are no lumbar spine red flags, and she does not report any swelling, heat, or redness.
- The patient denies having fever, unremitting night pain, or malaise.
- She is a vaper rather than a smoker.
- She reports no alcohol intake.
- Her PMH is unremarkable, and she takes no medications or reports any other health issues.
- A recent blood test revealed she is pre-diabetic.
Objective:
- Ankle AROM: reports no active Dorsiflexion.
- Neuro: Further evaluation is required during an in-person assessment.
Impression:
- The findings suggest foot drop, possibly related to slimmers palsy.
- The presentation appears consistent with common peroneal N palsy.
Face-to-face Assessment
Subjective:
- The patient reports no issues or pain with the lumbar spine, hip, or knee. She does not particularly feel pain in the foot or ankle but have noted a loss of power.
- Nil B&B incontinence, frequency issues, SA, or sciatica. The patient has been safety-netted for signs of CES.
- They deny appetite loss, fever, malaise, night sweats, or unremitting pain. GH is otherwise excellent.
- Deliberate weight loss following gastric surgery.
- There is no family history or personal history of Ca.
- Nil problems when supine, heavy legs, segmental pain, or heaviness in the legs other than power loss.
Objective:
- The patient exhibits an antalgic gait with a clear loss of dorsiflexion and a slapping foot.
- The Achilles reflex is absent, though reflexes are universally dull.
- Babinski and Hoffmann signs are negative.
- Sensation is reduced around the peroneal region extending into the dorsum of the foot, but sensation is otherwise normal.
- Lumbar spine, hip, knee AROM and power normal.
- SLR and slump tests are both negative.
- There is no pain on palpation of the fibular head or peroneal region.
Impression:
- The findings are consistent with common peroneal nerve palsy.
Treatment:
- The patient is currently wearing boots but has been advised to use an AFO in the short term for safety while awaiting further investigations.
Home Exercise Plan:
- The patient has been encouraged to attempt active dorsiflexion. No specific repetitions or sets as such.
Plan:
- An urgent MSK referral is required, with likely nerve conduction studies to follow.
After the face-to-face consultation, clinicians discussed the patient to determine the next course of action. An urgent MSK referral was completed with the thought that the patient needed Nerve Conduction Studies (NCS). After triage of the referral, MSK referred the patient for NCS. The GP also reviewed the patient at this point and requested an MRI of the spine to rule out any other causes of the foot drop.
Differential Diagnoses & Clinical Reasoning
After speaking with and examining the patient, the impression was consistent with common peroneal nerve palsy. At this point, before conducting further tests, it is important to consider other potential differential diagnoses:
1. L5 Radiculopathy
Although the patient has not reported any lower back pain, lumbar radiculopathy remains a possibility. Ordering an MRI, as requested by the GP, will help rule out lumbar pathology.
2. External Compression
Common peroneal nerve palsy may result from external nerve compression. Examples include:
- Leg crossing or contact sports
- Prolonged immobility: Bedridden patients often develop this neuropathy due to a combination of weight loss and pressure from hard hospital mattresses or bed railings.
- Plaster casts: A common cause of peroneal neuropathy.
None of these factors were identified as relevant during the patient’s subjective assessment.
3. Internal Compression
The nerve may also be compressed internally, leading to the palsy. Common causes include:
- Ganglions: Benign but infiltrative masses, often from the superior tibiofibular joint, that can compress or invade the nerve.
- Baker’s cysts: These can compress the common peroneal nerve and sometimes the tibial nerve.
- Tumors: Schwannomas and neurofibromas can arise anywhere along the common peroneal nerve or its branches, most frequently in the popliteal fossa. Other possibilities include calluses from old fibular fractures, osteomas, or malignant tumors in the fibular head or neck (Stewart, 2008).
At this stage, internal compression in the peripheral region has not been excluded.
4. Polyneuropathy
Diabetes is a major risk factor for polyneuropathy. Although this patient does not have diabetes, they were recently diagnosed with pre-diabetes via blood testing. This condition should be considered as a potential differential diagnosis.
5. Autoimmune Diseases
Autoimmune diseases have been ruled out based on the patient’s subjective assessment, with no signs of rheumatoid issues reported.
6. Infections
There were no indications of infection during the assessment (e.g., no fever, redness, swelling, or warmth). If concerns arise, a GP-requested blood test could help confirm or exclude infection.
Slimmer’s Palsy – Background
Physiology
The tibialis anterior, the main dorsiflexor muscle of the foot, is innervated by the peroneal nerve. This is derived from anterior horn cells in the lower spinal cord. Their axons travel in the L4 and L5 spinal nerve roots, and then join to form the lumbosacral trunk that connects these lumbar plexus structures to the sacral plexus.
These nerve fibres then join the lateral trunk of the sciatic nerve. When the sciatic nerve divides just above the knee, the lateral trunk continues as the peroneal nerve.
The peroneal nerve passes laterally through the popliteal fossa and winds around the head and neck of the fibula.
It is closely applied to the periosteum of that bone for about 6 cm. For most of this length, it is covered only by skin and subcutaneous tissue. It then penetrates the peroneus longus muscle to enter the anterior compartment of the lower leg. At this point, the muscle fibers form a tendinous arch over the nerve, known as the fibular tunnel.
The nerve supplies the tibialis anterior, the toe extensors, and the peroneal muscles. It also provides sensation to the skin on the anterolateral lower leg, starting from about midway between the knee and ankle, as well as most of the dorsal surface of the foot and toes.
When the nerve is lacerated at the knee, it causes widespread sensory loss across this area. In contrast, compression of the nerve results in a more localised sensory loss, typically limited to the dorsum of the foot and toes. (Stewart, 2008)
Summary
Slimmer’s Palsy is a rare condition in practice. As the prevalence of gastric banding surgery for weight loss increases, it is likely that this condition will become more commonly encountered. Awareness of this complication enhances confidence in managing affected patients and in educating those who may be unaware of its existence.
There is limited evidence on the causes of Slimmer’s Palsy beyond the known aetiology of CPN and the effects of sudden, drastic weight loss on subcutaneous tissue.
Although understanding of Slimmer’s Palsy has improved, it is essential to approach diagnosis cautiously. Normal referral and screening pathways must be followed to ensure that all other potential causes are thoroughly investigated before concluding that this condition is present.
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References
- Baharin, J., Yusof Khan, A.H.K., Abdul Rashid, A.M. et al. Slimmer’s palsy following an intermittent fasting diet. Egypt J Neurol Psychiatry Neurosurg 58, 157 (2022). https://doi.org/10.1186/s41983-022-00594-3
- https://www.nhs.uk/conditions/hereditary-neuropathy
- Sotaniemi, K. A. (1984). Slimmer’s paralysis–peroneal neuropathy during weight reduction. Journal of Neurology, Neurosurgery & Psychiatry, 47(5), 564-566.
- Stewart, J. D. (2008). Foot drop: where, why and what to do?. Practical neurology, 8(3), 158-169.
