Polyneuropathy - Neuropathy General Script

 

Thank you for asking me to examine Mr. X, who presented difficulty walking.

 

The most salient findings on examination were a high stepping gait (distal weakness) / proximal weakness (waddling gait) and a proximal/distal symmetrical/asymmetrical motor/sensory deficit, with/without associated motor/sensory loss, with upper / lower motor neuron signs, which would be most consistent with ____.

 

In further detail...

 

On inspection the patient was comfortable and did / did not have any gait aids. There were/were not any shoe or ankle supports.

 

The gait was ataxic and broad-based with stamping (proprioception loss) and high stepping (due to foot drop from distal motor neuropathy). The patient could/could not walk heel to toe, suggesting the presence/absence of a cerebellar pathology. The patient could/could not walk on their toes (S1), and the heels (foot drop, L4 or L5). Romberg’s sign was/was not positive (eyes closed - posterior columns, eyes open - cerebellar).

 

There were/were no scars on the back.

 

On inspection of the legs, there were/were not scars. There was/was not evidence of muscle wasting, and fasciculations, indicative of lower motor neuron pathology.

• For CMT - “there was distal wasting of the lower limbs, especially of the anterolateral muscle compartment with relative preservation of the thigh musculature, giving an inverted champagne bottle appearance’

• There was/was not bilateral pes cavus and clawing of the toes

 

There was/was not muscle tenderness. Tone was reduced/increased/normal in the knee and ankle, and there was/was not clonus. There was/was not an enlarged common peroneal nerve (CMT).

 

Power was normal/reduced symmetrical/asymmetrically with __/5 power on the left leg, and __/5 power on the right.

 

Reflexes were normal/reduced/absent/increased in the knee and ankle. Plantar response was upgoing/downgoing/inadequately assessed due to withdrawal.

 

Coordination was normal/impaired on heel-shin, toe-finger and foot tapping assessment.

Sensation was reduced/normal asymmetrical/symmetrically in a dermatomal/stocking distribution, with reduced sensation to pinprick to ____. There was normal/reduced vibrations sensation to ___. Proprioception as intact/impaired to the ___.

 

In summary this patient has a distal sensory/motor/sensorimotor, which is likely long standing given the presence of pes cavus and severe atrophy and suggests a hereditary neuropathy such as Charcot-Marie-Tooth.

 

Differential for a sensorimotor neuropathy include:

• Metabolic causes - primarily diabetes, CKD/uraemia, thyroid

• Drug and alcohol related - vincristine, cisplatinum

• B12 (or subacute combined degeneration - although strictly speaking not peripheral neuropathy - can present with weakness, reduced reflexes and dorsal column loss initially - only with time would you get spasticity)

• Immune mediate such as GB and CIDP - however, typically these have less sensory involvement, and no pes cavus, and are non-length dependent with proximal and distal muscles affected similarly

• Hereditary motor and sensory neuropathy

• Paraneoplastic - tumour, or paraproteinemia

• Connective tissue disease and vasculitis

• Idiopathic

 

Differential for a predominately motor neuropathy include:

• GBS/CIDP

• Hereditary motor and sensory neuropathy - CMT

• Diabetes

• Multifocal motor neuropathy

• Other - porphyria, lead, diphtheria, drugs (dapsone)

 

Differential for a predominately sensory neuropathy include:

• Metabolic - diabetes, uraemia/CKD, hypothyroidism

• Alcohol and drugs

• Paraneoplastic

• Vasculitic

• Sjogren’s syndrome

• Amyloidosis

 

I would have liked to complete my examination by:

• Neurological examination of upper/lower limbs

• Assessing for autonomic dysfunction with postural blood pressure

 

I would proceed from here by:

• Confirming my diagnosis with nerve conduction studies (low conduction velocity if demyelinating, low amplitude if axonal)

• Assessing for other aetiology by:

  • History, including drug history

  • Screen for diabetes, CKD, thyroid function

 

What would you be looking for a nerve conduction studies?

• We can test compound motor action potentials, and sensory nerve action potentials, and we can measure amplitude, distal latency and conduction velocity. Axonal neuropathies will typically cause decrease amplitudes. Demyelinating neuropathies will typically decrease conduction velocity and prolong distal latency. However, they can also cause decreased amplitude as there are fewer normally conducting axons. Area of demyelination can also cause focal slowing and a conduction block (e.g. carpal tunnel).

• For GBS, we can also assess the H-reflex and F-Wave. The H-reflex assesses the dorsal root by stimulating the tibial nerve and measuring the response in the soleus muscle. Prolonged latency is common in GBS. The F-Wave assesses the proximal portion of a motor nerve by antidromic conduction. Prolonged F-Wave latency can indicate proximal motor nerve or spinal cord pathology.

 

What about EMG?

• NCS can be complemented by electromyography, which assesses the electrical activity within skeletal muscles.

• Findings can be divided into those that occur with insertion of the needle (insertional activity), those that occur at rest (spontaneous activity), and those that occur with activation of the muscle (voluntary activity).

• In primary nerve disease, you may see increased spontaneous activity with denervation, such as fasciculation and fibrillation potentials. In terms of voluntary activity, you may see increase amplitude of motor unit action potentials as the surviving axons have to innervate a large number of motor fibers than they did previously. However, there are fewer overall motor units, and so there is reduced recruitment

• In primary muscle disease, on spontaneous activity, you won’t see fasciculations, although you may see myotonic discharges. On voluntary activity, there is reduced amplitude of motor unit action potentials, but more units are activated together early in muscle contraction, a pattern termed early recruitment.