Cauda equina syndrome (CES) is the spinal cord emergency most frequently litigated in UK practice — the cauda equina is the collection of L2-S5 nerve roots in the lumbar spinal canal below the conus medullaris (typically at L1-L2 level). Compression of these roots (most commonly by a massive L4/5 or L5/S1 disc prolapse, but also by tumour, haematoma, or abscess) causes the CES syndrome. The cardinal features are: bladder dysfunction (urinary retention — inability to void, or urinary incontinence from overflow retention), bowel dysfunction (faecal incontinence or constipation), saddle anaesthesia (numbness/reduced sensation in the perineum, buttocks, and inner thighs — the distribution of nerves that contact a saddle), and bilateral lower limb weakness and/or sciatica. The medicolegal risk: a GP who sends a patient with back pain + urinary symptoms home without specifically asking about saddle anaesthesia and arranging urgent MRI has potentially missed CES. The standard of care: any patient with back pain + any of: urinary retention, incontinence, saddle anaesthesia, or bilateral leg weakness, requires an emergency MRI spine and neurosurgical assessment.

The Babinski sign (upgoing plantar response) is the most important single clinical sign distinguishing upper from lower motor neurone pathology — it is elicited by slowly stroking the lateral sole of the foot from heel to ball with a blunt object (tongue depressor, key, or end of patella hammer). A normal adult response is plantar flexion of the great toe (downgoing) with or without flexion of the other toes. An upgoing plantar (Babinski positive) consists of dorsiflexion (extension) of the great toe with fanning of the other toes — this indicates damage to the corticospinal tract (UMN pathway) from any level between the motor cortex and the spinal cord segment supplying the foot. A positive Babinski in an adult with leg weakness = UMN pathology = MRI brain or spine urgently depending on associated signs. The caveats: Babinski is normally present in infants under approximately 18 months (immature corticospinal tracts); it may be difficult to elicit in patients with significant foot pain, severe peripheral neuropathy, or very anxious patients; a true positive requires the specific toe extension pattern, not just general withdrawal from tickling.

The MRC muscle strength grading scale (0-5) is the standard clinical tool for documenting motor weakness and tracking progression over time — it is essential for both diagnosis and medicolegal documentation: Grade 0 = No visible or palpable contraction; Grade 1 = Visible or palpable contraction but no movement; Grade 2 = Movement with gravity eliminated (horizontally); Grade 3 = Movement against gravity only (cannot resist any additional force); Grade 4 = Movement against gravity and some resistance (4- = minimal resistance, 4 = moderate, 4+ = good resistance); Grade 5 = Normal strength. In practice, most clinically significant weakness producing functional impairment will be grade 3-4. The distinction between grade 4 and grade 5 requires consistent application — a patient with MRC 4/5 hip flexion bilaterally who had previously normal strength has a significant finding that requires explanation. Documenting 'power normal' without specifying muscle groups and MRC grade is inadequate neurological documentation.

Foot drop (failure to dorsiflex the foot and toes — L4/L5 innervation via the common peroneal nerve) is one of the most common monosymptomatic presentations of leg weakness in primary care, and accurate localisation of the lesion is critical for correct management. The three anatomical sites causing foot drop that every GP must distinguish: (1) Peroneal nerve palsy at the fibular head (most common, from prolonged leg crossing, weight loss, casting, fibular fracture, or prolonged squatting): purely motor foot drop with no knee extension weakness, sensory loss over dorsum of foot + lateral calf, no reflex change — this is an LMN peripheral nerve lesion that often recovers spontaneously with removal of the compressive cause; (2) L5 radiculopathy (L4/5 disc prolapse): foot drop with sciatica (radiating to big toe), no ankle reflex change, positive SLR — requires MRI lumbar spine; (3) Cortical or corticospinal stroke (foot drop as part of hemiplegia): UMN signs, spasticity, hyperreflexia, upgoing plantar, associated arm weakness — requires urgent MRI brain. A GP who applies a foot drop brace without localising the anatomical cause has not adequately assessed the patient.

Malignant spinal cord compression (MSCC) is one of the most time-critical oncological emergencies and one that GPs can prevent or minimise disability from by proactive action — approximately 5-10% of cancer patients develop MSCC during their illness. The tumours most commonly responsible: lung (most common), breast, prostate, myeloma, kidney, colorectal. The clinical warning signs (PREMONITORY) that occur days to weeks before complete cord compression: back pain (the most common symptom — localised, constant, worse lying down at night, unlike mechanical back pain); progressive lower limb weakness; altered sensation in the legs; urinary frequency or retention. A cancer patient presenting with new back pain that is different from previous pain (constant, nocturnal, worsening) should trigger urgent MSCC assessment: dexamethasone 16 mg OD immediately (reduces cord oedema), MRI whole spine (same-day if available, next-day if not), and oncology/neurosurgery contact. The NICE guideline MSCC (NG91) is explicit: any suspected MSCC in a cancer patient = dexamethasone immediately, MRI same day, spinal cord compression nurse specialist involvement.

The IVIG vs plasmapheresis equivalence in Guillain-Barré syndrome is established by multiple RCTs and systematic reviews — both treatments are equally effective at reducing disability and time to recovery in moderate-severe GBS (defined as inability to walk unaided). The choice is made based on availability, local expertise, and patient factors: IVIG (intravenous immunoglobulin 0.4 g/kg/day for 5 days) is more widely available, easier to administer, and equally effective. Plasmapheresis (plasma exchange — 4-6 sessions over 1-2 weeks) requires a specialised centre and venous access. The critical principle: combination therapy (IVIG + plasmapheresis together) is NOT more effective than either alone. Steroids are CONTRAINDICATED in GBS — multiple RCTs show that steroids do not improve outcomes and may prolong the disease. This is one of the most important exceptions to the general principle of treating inflammatory neurological conditions with corticosteroids. GPs presenting a suspected GBS patient to the medical team should specifically mention 'no steroids for GBS.'

The dermatomyositis malignancy screen is a critical investigation that must not be omitted — dermatomyositis (characterised by proximal myopathy + heliotrope rash on the eyelids + Gottron's papules over the metacarpophalangeal joints + elevated CK) is associated with underlying malignancy in approximately 20-25% of adult cases (highest risk in patients over 45). The most commonly associated cancers: ovarian, lung, gastric, colorectal, breast, and non-Hodgkin's lymphoma. The malignancy may precede, coincide with, or follow the dermatomyositis diagnosis. Therefore, all adults with newly diagnosed dermatomyositis require a systematic malignancy screen: CT chest/abdomen/pelvis, CA-125 (women), PSA (men over 50), colonoscopy (over 50 or symptomatic), mammography (women over 40). The screen should be repeated annually for at least 3 years after diagnosis. GPs who diagnose or manage dermatomyositis must ensure this malignancy surveillance is completed and documented.

The DVLA notification requirement for leg weakness is a medicolegal obligation for GPs — the DVLA medical standards for fitness to drive (2021) specify that any condition causing limb weakness that affects vehicle control must be disclosed to the DVLA. The GP's responsibilities: (1) advise the patient verbally at the consultation that they have a legal obligation to notify the DVLA; (2) document this advice in the clinical record; (3) if a patient refuses to stop driving or notify DVLA despite the GP's advice, the GP should contact the DVLA directly (patient confidentiality can be breached in the public interest where there is a serious road safety risk, per GMC Good Medical Practice guidance). The relevant conditions: stroke causing significant weakness (must not drive for 1 month for car, longer for group 2), CES (must not drive until neurological recovery assessed), progressive neurological conditions (MS, MND) requiring regular DVLA notification and medical assessment for Group 2 licences. Driving assessment centres (approved by DVLA) can assess adapted vehicle control for patients who wish to continue driving with adaptations.

The dermatomyositis associated malignancy and the MSCC dexamethasone immediate prescription are two of the most important and high-stakes actionable clinical decisions in the management of leg weakness — they both illustrate that leg weakness is not just a rehabilitation challenge but a diagnostic investigation pathway with life-changing implications. GPs who approach leg weakness with a structured anatomical framework (UMN vs LMN, spinal vs peripheral, proximal vs distal), a systematic examination (tone, power, reflexes, sensation, coordination, plantars), and a low threshold for urgent MRI in new progressive weakness, will identify the serious and treatable causes before permanent neurological damage occurs. The single most important clinical principle in leg weakness: any progressive leg weakness without a clear established cause needs urgent investigation — 'watchful waiting' is not appropriate for new progressive neurological weakness.