In motor polyneuropathies, muscle strength and tendon reflexes decrease symmetrically, in sensorimotor polyneuropathies appear additionally skin sensation deficits (sock or glove type of distribution), and muscle atrophy develops later in the distal parts of the extremities.
Generally symmetrical muscle weakness, progressing from the distal parts of the limbs upwards, developing within a few days or over a few weeks' time. The chronic form progresses more slowly. Frequently there is myalgia in the extremities, and tendon reflexes decrease.
Radiculopathies, damage to one or more nerve roots
The cardinal symptom is radiating pain. Additionally, paraesthesia and numbness occur in the dermatome innervated by the nerve root.
Increasing muscle weakness in the muscles innervated by the affected nerve and decreased segmental tendon reflexes. When the condition has become chronic, muscle atrophy develops.
Damage to neural plexus, plexus injury, plexus neuritis
Symptoms include acute myalgia followed by sensory deficits, muscle weakness, decreased tendon reflexes, and muscle atrophy, which appear in one or more segments of the peripheral nerves involved in the plexus.
These include congenital muscular dystrophies, metabolic myopathies, inflammatory myopathy (myositis), as well as toxic (e.g. alcoholic myopathy) and endocrine myopathies.
Periodic paralyses: sporadic attacks of flaccid paralysis
Hypokalaemic: teenage onset
Hyperkalaemic: childhood onset
Normokalaemic: childhood onset
The myasthenic attack is often preceded by muscle strain or a meal high in carbohydrates.
Other endocrinological and metabolic causes
Hypo- or hyperthyroidism and hypo- or hypercalcaemia may be associated with muscle weakness.