Limb weakness

Limb weakness is a common presenting symptom in neurology and general practice, affecting individuals of all ages.
The prevalence increases with age, with a higher incidence in patients with comorbid conditions such as diabetes, stroke, and multiple sclerosis.
It can result from a wide range of conditions, from benign to life-threatening, necessitating careful evaluation.
Limb weakness can be due to central nervous system disorders, peripheral nervous system disorders, muscle diseases, or systemic conditions.
The burden of disease varies globally, with higher rates in populations with limited access to healthcare and higher rates of vascular risk factors.

Central Nervous System Causes

Stroke: Sudden onset of limb weakness, typically unilateral, with or without other neurological deficits.
Multiple Sclerosis: Relapsing-remitting weakness, often associated with other symptoms like optic neuritis and sensory changes.
Spinal Cord Compression: Can cause bilateral limb weakness, often with sensory changes below the level of the lesion.
Brain Tumor: Gradual onset of limb weakness, often with other signs of raised intracranial pressure.
Cerebral Palsy: Non-progressive motor disorder beginning in early childhood, characterized by spasticity and limb weakness.
Motor Neuron Disease (ALS): Progressive weakness with muscle atrophy and fasciculations, usually starting distally.
Transverse Myelitis: Acute or subacute spinal cord inflammation causing bilateral limb weakness, often with bowel/bladder dysfunction.
Cerebral Palsy: Non-progressive motor disorder from early childhood, characterized by spasticity and limb weakness.
Guillain-Barré Syndrome: Ascending, symmetrical weakness, often following an infection, with absent reflexes.
Parkinson’s Disease: Limb weakness as part of generalized bradykinesia, rigidity, and tremor.

Peripheral Nervous System Causes

Peripheral Neuropathy: Commonly caused by diabetes, presenting with distal limb weakness and sensory loss.
Radiculopathy: Compression of nerve roots, often causing unilateral limb weakness with radicular pain.
Carpal Tunnel Syndrome: Median nerve compression leading to weakness and atrophy of the thenar muscles.
Bell’s Palsy: Facial nerve paralysis causing weakness of the muscles on one side of the face.
Myasthenia Gravis: Autoimmune disorder causing fluctuating muscle weakness, often worsened by activity and improved by rest.
Polyneuropathy: Often seen in conditions like chronic alcoholism, leading to symmetric distal limb weakness.
Diabetic Amyotrophy: A painful, asymmetrical motor neuropathy affecting the thighs and hips, seen in diabetics.
Entrapment Neuropathy: Compression of peripheral nerves (e.g., ulnar or radial nerves) leading to localized limb weakness.

Muscular Causes

Muscular Dystrophy: Genetic disorders causing progressive muscle weakness and wasting, often starting in childhood.
Polymyositis: Inflammatory myopathy causing proximal muscle weakness and raised muscle enzymes.
Dermatomyositis: Similar to polymyositis, but with characteristic skin rashes.
Rhabdomyolysis: Muscle breakdown leading to weakness, myoglobinuria, and raised creatine kinase.
Inclusion Body Myositis: A slowly progressive inflammatory myopathy affecting the elderly, with both proximal and distal muscle weakness.
Statin-induced Myopathy: Muscle weakness and pain caused by statin use, usually reversible upon cessation.
Hypokalemic Periodic Paralysis: A rare condition causing episodic muscle weakness due to low potassium levels.
Thyrotoxic Myopathy: Muscle weakness due to hyperthyroidism, often improving with treatment of the underlying condition.
Fibromyalgia: Chronic condition characterized by widespread pain, fatigue, and muscle tenderness, sometimes perceived as weakness.
Myotonic Dystrophy: Genetic disorder causing muscle stiffness (myotonia) and weakness, along with systemic features.

Background

Onset and Duration: Determine whether the weakness is acute, subacute, or chronic.
Progression: Ask about how the weakness has progressed and whether it is fluctuating or steadily worsening.
Symmetry: Ascertain whether the weakness is unilateral, bilateral, or asymmetric.
Associated Symptoms: Inquire about pain, sensory changes, sphincter disturbances, or systemic symptoms like fever or weight loss.
Risk Factors: Identify risk factors such as recent infections, vaccination, trauma, or exposure to toxins.
Family History: Ask about any family history of neurological or muscular diseases.
Medication History: Note any medications that could contribute to weakness, such as statins or steroids.
Past Medical History: Include relevant conditions such as diabetes, vascular disease, or previous strokes.
Social History: Consider occupational exposure, physical activity levels, and substance use.
Functional Impact: Assess how the weakness affects daily activities, mobility, and independence.
Psychiatric History: Explore any history of mental health issues, as depression and anxiety can present with perceived weakness.

Clinical Examination

Neurological Examination: Assess muscle strength, tone, reflexes, and coordination to localize the lesion.
Sensory Examination: Check for sensory deficits, which can help differentiate between central and peripheral causes.
Gait Assessment: Observe the patient’s gait for any abnormalities that could suggest a specific diagnosis.
Cranial Nerve Examination: Particularly important in cases where the weakness is associated with facial or bulbar symptoms.
Cardiovascular Examination: To rule out vascular causes such as stroke or peripheral arterial disease.
Musculoskeletal Examination: Check for signs of joint inflammation, muscle atrophy, or tenderness.
Skin Examination: Look for rashes, ulcers, or other dermatological signs that could suggest systemic disease.
Respiratory Examination: Consider in cases where weakness is associated with conditions like Guillain-Barré Syndrome.

Laboratory Tests

Full Blood Count (FBC): To identify any underlying infection, anemia, or hematological cause.
Electrolytes: Particularly potassium, calcium, and magnesium, which can affect muscle function.
Thyroid Function Tests: To rule out hypothyroidism or hyperthyroidism as causes of muscle weakness.
Creatine Kinase (CK): Elevated in muscle diseases such as polymyositis or rhabdomyolysis.
Autoantibodies: For suspected autoimmune conditions like myasthenia gravis or lupus.
ESR/CRP: Elevated in inflammatory or infectious conditions causing limb weakness.
Vitamin B12 and Folate: Deficiencies can lead to peripheral neuropathy and weakness.
Toxicology Screen: Consider in cases of suspected drug or toxin-induced weakness.
Lactate and Pyruvate: To evaluate for mitochondrial disorders if suspected.
Lumbar Puncture: Consider in cases of suspected Guillain-Barré Syndrome or CNS infection.
Electromyography (EMG) and Nerve Conduction Studies: Useful in diagnosing neuromuscular disorders.
Genetic Testing: For conditions such as muscular dystrophy or myotonic disorders.

Cardiovascular