A gait change rarely announces itself. Patients describe it in half-sentences - "I feel a bit off when I turn", "my left leg is not doing what my right leg is doing", "I nearly went over on the pavement". Balance is the first thing to break silently, and the last thing anyone tests properly. This piece is a plain-English guide to when a change in walking or balance needs an MRI, and which MRI to book when it does.
The stakes are not small. A cerebellar stroke, a compressed cervical cord, or normal pressure hydrocephalus can all present as "just getting a bit unsteady". All three are treatable if caught. All three are missable if the wrong scan, or no scan, is ordered.
One-line answer
If balance change or gait change is new, progressive, or comes with any neurological symptom, you need an MRI of the brain, and often of the cervical spine as well - and you need it in weeks, not months.
Peripheral vs central: HINTS at the bedside
Before any scan, a good clinician tries to separate a peripheral (inner-ear) cause from a central (brain or brainstem) cause. The HINTS exam - Head Impulse, Nystagmus, Test of Skew - is a three-part bedside test that, in expert hands, is more sensitive than an early MRI for posterior circulation stroke. In practical terms:
- Peripheral pattern: sudden vertigo, one-direction horizontal nystagmus, a normal head-impulse test, no other neurology. Usually vestibular.
- Central pattern: vertical or direction-changing nystagmus, a normal head-impulse test on the vertiginous side, skew deviation, or any additional neurological finding. Assume brain until proven otherwise.
If any part of HINTS is central, MRI of the brain with diffusion-weighted imaging is the correct next test, and it should happen the same day if the symptoms are new.
Red flags that need an MRI now
Some presentations are not for the routine GP queue. Any of the following turns a "let us watch and wait" into a "scan this week":
- An associated neurological deficit - weakness, numbness, slurred speech, double vision, swallowing difficulty, a droopy face.
- Sudden onset - balance was fine on Tuesday, gone on Wednesday. Sudden means vascular until proven otherwise.
- Older adult with vascular risk factors - hypertension, atrial fibrillation, diabetes, smoking history, previous TIA or stroke.
- A new headache, particularly at the back of the head, or worsening on coughing, straining or lying flat.
- Ataxia when eyes are open - if the world does not steady when you look at it, that is usually cerebellar.
- A history of cancer - metastasis to the cerebellum or brainstem presents exactly like this.
What a brain MRI actually reveals in gait and balance problems
A well-protocolled brain MRI in this setting is not a single image - it is a set of sequences chosen to answer specific questions. In an adult with new or progressive gait change, the report is looking at:
- Cerebellar stroke or atrophy. A small infarct in the posterior inferior cerebellar artery territory can look mild clinically and be catastrophic if a second one lands. Chronic cerebellar atrophy points to degenerative causes.
- Small vessel disease. White matter hyperintensities and lacunar infarcts - the accumulated damage of years of unmanaged blood pressure - are one of the commonest causes of the "cautious, wide-based, older-adult gait".
- MS plaques. Demyelinating lesions in the brainstem, cerebellar peduncles or spinal cord, in someone under 50, with intermittent symptoms.
- Normal pressure hydrocephalus. Enlarged ventricles out of proportion to cortical shrinkage, with the classic clinical triad of gait, urinary urgency and cognitive change. Treatable with a shunt in selected patients.
- Posterior fossa mass. Rare, but not vanishingly so - a tumour, a metastasis, or a Chiari malformation can present as a slowly worsening balance problem.
What a brain MRI does not do well is diagnose Parkinson's disease itself, which is a clinical diagnosis. But it does rule out the mimics - vascular parkinsonism, NPH, atypical parkinsonian syndromes - that a movement disorder neurologist will want excluded before starting long-term treatment.
The role of cervical spine MRI
Cervical myelopathy is one of the most under-diagnosed causes of gait change in adults over 55, and it is a structural, mechanical problem that responds to treatment if caught before the cord is permanently injured. The pattern is a slow, stiff, unsteady walk, with brisk reflexes, arm and hand clumsiness (dropping cups, buttons becoming hard), and often neck stiffness. Reflexes are the tell - upper motor neuron signs (brisk knee jerks, upgoing plantars, clonus) in someone with a walking problem should always prompt a cervical spine MRI.
The scan looks for spondylotic narrowing of the spinal canal, disc protrusions, ossification of the posterior longitudinal ligament, and, most importantly, signal change within the cord itself - which is the marker that the compression is causing damage, not just narrowing. In practice, when the clinical picture is mixed, a combined brain and cervical spine MRI is often the most efficient single booking.
We routinely see patients in their sixties who were told for two years that they were "just getting older". They had cervical myelopathy, visible on a fifteen-minute sequence, and by the time it was found the cord change was permanent.
