Weakness on One Side of the Body — What Is Causing It?
Sudden weakness in one arm or leg, or one side of the face. This is a medical emergency until a stroke is ruled out. Act FAST.
One-sided weakness — hemiparesis (partial) or hemiplegia (complete paralysis) — is one of the most important neurological symptoms you can experience. When it develops suddenly, it must be treated as a stroke until proven otherwise. Early neurological assessment and CT brain scan are essential to determine the cause and guide immediate treatment. Time is brain — every minute of delayed treatment in a stroke destroys approximately 1.9 million neurons.
Key Points
- Sudden one-sided weakness must be treated as a stroke until proven otherwise — call 108 immediately.
- Remember FAST: Face drooping, Arm weakness, Speech difficulty, Time to call emergency services.
- Clot-busting treatment is only effective within 4.5 hours of stroke onset — every minute counts.
- A TIA (weakness that recovered within 24 hours) still carries a 10% risk of major stroke within 48 hours — requires urgent evaluation.
- Not all one-sided weakness is stroke — Todd's paralysis, MS, and hypoglycaemia are other causes a neurologist will identify.
1.9M
brain cells die per minute of untreated stroke
Source: AHA / ASA
4.5 hrs
window for thrombolysis treatment
Source: AHA Stroke Guidelines
80%
of strokes are preventable with risk factor control
Source: WHO / ISA
"Sudden one-sided weakness is a stroke until proven otherwise in my clinic. The time the weakness started is the most critical piece of information — it determines whether we can use clot-busting treatment. Act FAST, call 108, and let me handle the diagnosis."
Seek Emergency Care Immediately If You Have:
- 1Sudden onset weakness on one side of the body
- 2Weakness accompanied by face drooping or speech difficulty
- 3Any one-sided weakness in a person with diabetes, high blood pressure, or atrial fibrillation
- 4Weakness after a headache — even if mild
- 5Progressive worsening weakness over hours or days
Possible Causes of This Symptom
Stroke (Ischaemic or Haemorrhagic)
The most important cause of sudden one-sided weakness. Caused by a blocked artery (ischaemic stroke) or bleeding in the brain (haemorrhagic stroke). Requires immediate emergency evaluation.
TIA (Transient Ischaemic Attack)
A brief stroke that resolves completely within 24 hours. May cause one-sided weakness lasting minutes to hours. HIGH risk of major stroke within 48–72 hours — emergency assessment is essential even after recovery.
Todd's Paralysis (Post-Seizure)
Temporary one-sided weakness lasting hours after a focal seizure. Caused by neuronal exhaustion in the motor cortex. Resolves spontaneously — but the underlying seizure cause needs evaluation.
Multiple Sclerosis Relapse
MS can cause one-sided weakness as part of a relapse, typically developing over hours to days (slower than stroke). Other neurological symptoms (sensory changes, optic neuritis) may accompany it.
Space-Occupying Lesion (Tumour, Abscess)
A brain tumour or abscess causing gradual weakness developing over weeks to months. Associated with headache, personality changes, or seizures. Requires urgent brain imaging.
How We Diagnose the Cause
Urgent Neurological Assessment
Full motor, sensory, coordination, and cranial nerve examination to localise the weakness and determine urgency.
CT Brain (Emergency)
CT brain immediately distinguishes haemorrhagic from ischaemic stroke — critical for treatment decisions. Arranged as an emergency.
Blood Tests and ECG
Blood glucose, FBC, coagulation, lipids, ECG (for atrial fibrillation) — identifying metabolic causes and stroke risk factors.
Your Treating Specialist
Sri Anand Child and Neuro Center, Chanda Nagar, Hyderabad
In-house EEG and NCS — same-visit diagnosis, no referral delays
Frequently Asked Questions
Related Pages
Book Your Consultation Today
Sri Anand Child & Neuro Hospital · Open 24/7 · Chanda Nagar, Hyderabad