● Peripheral nerve lesions
● Peripheral nerve compression
● Motor neuropathy
● Peripheral nerve transection
● Disuse atrophy
● Anterior horn cell lesions
● Previous poliomyelitis (common in developing
● Vitamin D deficiency
● Cardiac and/or respiratory cachexia
● Guillain–Barré syndrome
● Cushing’s disease
● Addison’s disease
MUSCLE AND MOTOR END PLATE DISORDERS
● Myasthenia gravis
● Muscular dystrophies
● Motor neurone disease
● Myotonic dystrophy
● Polymyositis/dermatomyositis/inclusion body myositis
DRUGS AND TOXINS
Muscle weakness and wasting in childhood is often due to congenital
disease such as inherited muscular dystrophies (e.g. Duchenne’s
muscular dystrophy), a diagnosis further supported by a positive
family history of a first-degree relative with similar problems. With
myotonic dystrophy, first symptoms occur around the age of 15–30
years, while with motor neurone disease, the peak age of onset is in
the 50 s.
The distribution of muscle wasting may characterise the disease.
Atrophy may be confined to the motor supply of a single nerve, such
as the thenar eminence with the median nerve affected by carpal
tunnel syndrome. It may also occur with a group of muscles such as
the leg, with polio. The distribution may be generalised in conditions
such as motor neurone disease. Distal weakness ascending to involve
proximal muscles is characteristic of Guillain–Barré syndrome.
Precipitating factors such as trauma may result in transection of a
peripheral nerve such as the ulnar nerve, commonly at the wrist.
Past medical history
The presence of carcinoma or chronic cardiorespiratory disease
may give rise to peripheral muscle wasting from cachexia. Previous
infection with polio is significant because, in a minority of affected
individuals, degeneration of anterior horn cells with subsequent
paralysis and muscle wasting occurs (post-polio syndrome). Disuse
atrophy can be localised or generalised. Conditions that result in
immobility such as a long-bone fracture will cause disuse atrophy
of the surrounding muscles; this is commonly seen upon removal of
plaster casts. Localised disuse atrophy may also result from joint pains
such as quadriceps wasting with painful knee disorders. Prolonged
immobility will result in generalised muscle wasting. Conditions such
as diabetes and renal failure are associated with neuropathy. Poor
diet and lack of sun exposure may lead to vitamin D deficiency.
Most of the causes are associated with weakness of the affected
muscles. Diplopia, ptosis and fatiguability are associated features
suggestive of myasthenia gravis. Motor neurone disease may
present with progressive weakness and wasting of the hand or leg
accompanied with dysarthria and dysphasia. Cushing’s disease may
be associated with weight gain, hair growth, acne, abdominal striae,
muscle weakness, back pain and depression.
Inspection will identify the areas of muscle wasting. Central obesity
with limb wasting occurs with Cushing’s disease. Generalised uniform
muscle wasting should lead to a careful examination of the organ
systems for malignancy and organ failure. Muscle tenderness may
occur with polymyositis.
Characteristic features of myotonic dystrophy are frontal balding,
ptosis, temporal and facial muscle wasting. Cataracts may be
seen with inspection of the eyes. Ptosis may also be a feature of
myasthenia gravis; this is accompanied by diplopia, facial weakness
and a weak nasal voice. Muscle wasting with fasciculations occurs
with motor neurone disease, no sensory loss is experienced and
mixed upper and lower motor neurone signs may be present.
Assessment of tone, reflexes and pattern of weakness will
determine whether it is an upper or lower motor neurone lesion.
Delayed relaxation of muscle contraction occurs with myotonic
dystrophy and proximal muscle weakness occurs with Cushing’s
disease. With localised muscle wasting, examination of each muscle
will allow you to determine whether the lesion arises from a single
nerve or a nerve root. Weakness, areflexia and sensory loss are seen
with Guillain–Barré syndrome.
The joint surrounded by wasted muscles should be examined for
deformity or pain that may restrict movement. Measurements of
circumference can be obtained to assess asymmetrical muscle wasting
of the limbs.
Proximal muscle weakness may be more evident than distal weakness
in many of the conditions listed. Specific assessment for this, such as
rising from a low chair or from a squatting position, is required.
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