Weakness

This is Skunk Anansie lead singer, Skin, who wrote the song Weak. It's a good song and better than Bell's palsy.

Definition

Reduction in power of motor system.

Epidemiology

Pathophysiology

Essentially, either you're just knackered and suffering from fatigue due to systemic illness. Neurological causes result in specific patterns of weakness, firstly differentiating between focal and local and between upper and lower motor neuron.

Clinical and Associated Features

• Fatigue - generalised all-over weakness is due to any systemic illness.
• Lower motor neurone (LMN) lesion - generally, this will be in the distribution of a specific nerve (e.g. wrist drop in a radial nerve palsy). Results in: wasting, reduced tone, reduced reflexes. No sensory loss in pure LMN lesion.
• Upper motor neurone (UMN) lesion - not specific to a nerve but maybe a nerve root or part of the brain (e.g. in stroke). Results in: fasciculations, potentially wasting, increased tone, hyperreflexia (brisk reflexes).
• Proximal muscle weakness - generalised weakness in the big muscles. This tends to happen over time. Muscle bulk depends on the aetiology.

Differential Diagnosis

• Fatigue due to systemic illness in generalised weakness
• UMN lesion - CVA (though check out the stroke page for specific syndromes and their causes), motor neurone disease
• LMN lesion - trauma
• Proximal muscle weakness - genetic (myasthenia gravis, Duchenne); connective tissue disorders (polymyositis, dermatomyostis); thyroid (hyper- and hypothyroidism; corticosteroid (steroid therapy, Cushing's, Conn's); electrolyte disturbance (hypo- & hyperkalaemia, hypercalcaemia, hypomagnaesia).