Makindo Medical Notes

Limb weakness can arise from various neurological, muscular, or systemic conditions. A systematic approach, combining a detailed history, physical examination, and relevant investigations, is essential for determining the underlying cause. Below is an outline of important considerations when assessing the causes of limb weakness.

History

• Onset: Sudden, gradual, or episodic onset helps in differentiating between acute and chronic conditions. Sudden onset may indicate stroke, while gradual onset could suggest degenerative or muscular diseases.
• Duration: The duration of weakness (acute vs. chronic) provides clues to the diagnosis. Chronic progressive weakness may suggest motor neuron disease or muscular dystrophy.
• Associated Symptoms: Look for pain, sensory disturbances, fatigue, and constitutional symptoms like fever or weight loss. Sensory loss suggests nerve involvement, while pain may indicate inflammatory or compressive causes.
• Pattern of Weakness: Proximal (e.g., shoulders, hips) weakness often points to muscular or metabolic causes, while distal weakness (e.g., hands, feet) may suggest neuropathy or motor neuron disease.
• Precipitating Events: Recent infections, trauma, or exposure to toxins or drugs can point towards causes such as Guillain-Barré syndrome, traumatic injury, or medication-induced myopathy.
• Family History: A family history of neurological disorders or muscular dystrophies may indicate a genetic cause of weakness.

Physical Examination

• Muscle Strength Testing: Assess the degree of weakness using the Medical Research Council (MRC) scale from 0 (no movement) to 5 (normal strength).
• Reflexes: Increased reflexes may suggest an upper motor neuron lesion (e.g., stroke), while absent or diminished reflexes point to a lower motor neuron lesion (e.g., peripheral neuropathy).
• Muscle Bulk and Tone: Look for signs of muscle atrophy (suggesting chronic disease), fasciculations (pointing to motor neuron disease), or hypertonia (suggesting central nervous system involvement).
• Coordination: Test for cerebellar dysfunction (e.g., dysmetria, intention tremor) which may indicate a central cause of weakness.
• Gait Assessment: Evaluate the patient's gait for patterns like foot drop (peripheral neuropathy) or waddling gait (proximal muscle weakness).

Common Causes of Limb Weakness

• Neurological Causes: Stroke, multiple sclerosis, motor neuron disease, peripheral neuropathy, Guillain-Barré syndrome.
• Muscular Causes: Muscular dystrophy, myositis, metabolic myopathies (e.g., glycogen storage diseases).
• Spinal Cord Pathology: Compression (e.g., herniated disk, tumour), transverse myelitis, trauma.
• Autoimmune and Inflammatory Disorders: Myasthenia gravis, polymyositis, dermatomyositis, lupus.
• Metabolic and Endocrine Disorders: Hypokalemia, hyperthyroidism, Cushing's syndrome, diabetes-related neuropathy.
• Toxins and Drugs: Alcohol, statins, steroids, chemotherapeutic agents (e.g., vincristine).

Diagnostic Investigations

• Blood Tests: Include complete blood count (CBC), electrolytes, creatine kinase (CK), thyroid function tests, and autoimmune markers.
• Neuroimaging: MRI or CT of the brain and spinal cord to rule out stroke, tumours, or compressive lesions.
• Nerve Conduction Studies and Electromyography (EMG): Assess peripheral nerve function and identify neuropathy, motor neuron disease, or myopathy.
• Muscle Biopsy: Useful for diagnosing muscular dystrophy, inflammatory myopathies, or metabolic disorders.
• Lumbar Puncture: For suspected central nervous system infections, multiple sclerosis, or Guillain-Barré syndrome.

By carefully evaluating the history, clinical examination, and diagnostic tests, clinicians can identify the specific cause of limb weakness and tailor treatment accordingly.

Causes of Limb Weakness