Neuromuscular disease patterns

Main patterns in neuromuscular disease:


Often you will be able to determine that the lesion responsible for the patients symptom is not in the brain or spinal cord but likely represents a neuromuscular disease. This section is to help you further localize the lesion when you suspect neuromuscular disease.
Neuromuscular disease include peripheral nervous system diseases, neuromuscular junction disorders or muscles diseases (myopathies). Peripheral nervous system diseases include all disease of nerves i.e. the somatic (motor and sensory) nervous system as well as the autonomic nervous system. This section gives a brief overview of these 3 main categories.
Once you localize the disease to a neuromuscular condition, knowing the main pattern of neuromuscular dysfunction can help you localize the lesion further. This is important as the number of neuromuscular disorders is very large. Luckily, a few simple points allow us to approach patients with suspected neuromuscular disease. One of these is obtaining a good history and clinical exam for sensory features (numbness, paraesthesia, vibration loss and impaired proprioception). For example the presence of sensory symptoms quickly allows us to exclude myopathies and neuromuscular disorders from the differential diagnosis. On the other hand, the absence of sensory symptoms or signs narrows the differential to motor neuron diseases, pure motor neuropathies, neuromuscular disorders or myopathies.
Like with any localization the distribution of dysfunction is important. Which limbs are involved? Just one limb, or more? Are the findings distal or proximal? Does this fit with a radicular pattern indicating nerve root disease or a peripheral nerve pattern indicating mononeuropathy, or is the pattern something else?
Another feature to assess is the presence or absence of reflexes. Also, note the relationship between the reflexes and the motor strength of the muscle group. Are the reflexes diminished out of proportion to the muscle weakness? This suggests nerve disease. Furthermore, this would suggest demyelinating nerve disease over axonal nerve disease. Lastly, remember that nerve diseases are much more common than neuromuscular junction disorders or myopathies.
Please review some of these patterns and tips along with the relevant neuroanatomy and correlate with the patients you see. It takes some time but this effort will pay off. It is helpful to go back and forth between assessing your patient by history and physical exam and reading the following sections:

  • Approaching weakness, approaching sensory deficits, neuromuscular patterns
  • The individual diseases

Here are the steps to localizing within neuromsuclar disease:

  1. Consider if the presentation may be a neuromuscular disease (see approach to weakness, approach to sensory deficits)
  2. Try to localize within the main 3 categories nerve, neuromuscular junction or muscle based on distribution of findings and presence of sensory findings
  3. If it is a nerve disorder try to localize within the main patterns of nerve disease. If it is a myopathy try to localize within the main patterns of myopathy. Neuromuscular junction disorders tend to have fairy characteristic syndromes, but they may be confused with either neuropathy or myopathy.
  4. After you localize, then think about etiologies and come up with the differential diagnosis to guide your investigation and treatment plan.

Localization in Peripheral Nervous system – Nerve diseases patterns:

Cranial neuropathy:

  • Diseases of one or more of the cranial nerves II-XII
  • It is important to distinguish between cranial neuropathies and diseases of the brainstem
  • There should be no “long tract signs”. This refers to the ascending and descending tracts through the brainstem. There should not be signs suggesting corticospinal tract, spinothalamic tract etc. Also there should be no cerebellar signs

Alpha motor neuron:

  • Fasciculations
  • Atrophy
  • Usually develops asymmetrically i.e. starts in one limb, subdquently other limbs are affected, so at a late stage it affects all the limbs
  • May develop in the bulbar muscles first; causing dysphagia, dysarthria
  • Progresses to involve the phrenic nerve and nerves supplying the accessory muscles of respiration
  • Very importantly, there is no sensory deficit
  • In amyotrophic lateral sclerosis (ALS), the most common motor neuron disease, the UMN is involved as well

Peripheral nerve:

  • Radiculopathy:
    • Lower motor neuron (LMN) lesion due to nerve root disease
    • In other words, the deficit conforms to the segmental innervation of the affected motor or sensory roots
    • Motor, sensory or both
    • Sensory modalities e.g. Pain may be a feature, for example sciatica with weakness
  • Plexopathy (brachial or lumbosacral):
    • Lower motor neuron (LMN) lesion due to damage of a plexus (brachial or lumbo-sacral)
    • The deficit that does not conform to mononeuropathies or polyneuropathy
    • Motor, sensory or both
    • Upper arm and shoulder involvement in upper branchial plexus lesions, forearm and hand involvement in lower brachial plexus lesions.
  • Mononeuropathy:
    • LMN lesion due to single nerve disease
    • The deficit conforms to the distribution of a single nerve, e.g. ulnar nerve palsy or radial nerve palsy, median nerve palsy
    • Motor, sensory or both
    • Sometimes the nerve is palpable
    • Tinel’s phenomenon may occur: tapping the nerve causes a tingling sensation
  • Mononeuropathy multiplex (Mononeuritis multiplex):
    • LMN lesion that begin like a mononeuropathy, but other nerves then become involved
    • Therefore it starts asymmetrically i.e. in one arm then progresses to involve other nerves in other limbs
    • If seen at the late stage, the disease is diffuse and symmetrical. Therefore the history and progression is important in this case
    • Sometimes the nerve is palpable
    • Motor, sensory or both
    • Tinel’s phenomenon may occur: tapping the nerve causes a tingling sensation
  • Polyneuropathy:
    • Develops symmetrically and distally leading to a glove and stocking distribution
    • It doesn’t fit into a nerve root (segmental) or multiple peripheral nerve distribution
    • Motor, sensory or both
    • If sensory: small fibres, large fibres or both
    • Small fibres: decreased pinprick and temperature sensation (painful and burning), autonomic dysfunction, but with normal power and reflexes
    • Large fibres: areflexia, sensory ataxia
  • Small fiber neuropathy:
    • May present with paresthesia, dysesthesia or loss of sensation to pain. Autonomic dysfunction can also occur because some autonomic fibres are also small unmyelinated fibres.
    • Decreased pinprick and temperature sensation (painful and burning), autonomic dysfunction, but with normal power and reflexes
  • Autonomic neuropathy:
    • Presents with features of autonomic dysfunction: orthostatic hypotension, gastroparesis, constipation, erectile dysfunction, impaired sweating etc
    • May also have features of somatic small fibre neuropathy (see above)

Neuromuscular junction disorders features:

  • No atrophy
  • Normal or reduced tone
  • Weakness: patchy i.e. doesn’t conform to an anatomic structure, fluctuation with time and exercise i.e. fatigability
  • Normal or depressed reflexes
  • No sensory changes
  • Fatigability of weakness or facilitation of power. Weakness that gets worse or better with muscle exertion.

Myopathy features:

  • Muscle may be normal, wasted or pseudohypertrophied, depending on the disease and time of presentation
  • Weakness, usually more proximal than distal
  • Usually proximal rather than distal weakness, but there are distal myopathies. Also, some myopathies are restricted to certain muscle groups e.g. ocular and pharygeal muscles
  • Usually symmetric weakness
  • Pure motor weakness without sensory signs
  • Tendon reflexes are usually preseved until late in the disease. They may be depressed later on in the disease. Normal abdominal and plantar reflexes
  • Make an attempt to characterize which muscle groups are affected: upper limb shoulders girdle (deltoids,  rotator cuff), lower limb girdle (gluteal, quadreceps), distal muscles (finger flexors, peroneal muscles), occular muscles, pharyngeal muscles, diaphgram or heart.
  • Bowel and bladder sphincters are usually spared.


Patterns for localising motor or sensory deficits:

Lateralised symptoms (e.g. hemiparesis):

  • Hemispheric lesions
  • Thalamus
  • Brain stem
  • Less commonly, spinal cord
  • Associated with cortical signs (aphasia, apraxia, visual field defect):
    • Think of hemispheric lesions
  • Associated cranial nerve dysfunction (vertigo, diplopia, dysarthria, ataxia):
    • Think of brainstem lesions

Cranial nerve abnormalities:

One limb or Part of a limb is affected:

All limbs are affected:

Only lower limbs affected:


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