see also:

• neurology¹⁾
• pruritus or itching
• touch
• pain

• numbness may be caused by a multitude of aetiologies ranging from central pathologies involving the brain or spinal cord, peripheral nerve pathologies either involving only one nerve or a number of them, or metabolic abnormalities such as hypocalcaemia or toxins.
• it is thus critical to determine an anatomic pattern where possible to better target the most likely possibilities.
  • see sensory & motor testing including dermatomes, myotomes, reflexes, coordination & balance
• it is also important to determine what the patient means - sometimes patients will say their face is feeling funny or numb when in actual fact they have a facial nerve palsy which is motor weakness.
• finally, patients may have psychogenic numbness as part of their conversion illness and often occurs as a glove and stocking pattern with a sharp demarcation - try testing pin prick with patient's fingers interlocked to confuse them.

• perhaps one of the most common patterns seen which is usually due to anxiety-induced hyperventilation causing a relative hypocalcaemia due to the respiratory alkalosis, and this results in pins and needles sensation mainly involving circum-oral region (lips), bilateral fingers and possibly toes.
• if hypocalcaemia is severe, there may be associated carpopedal spasm and other features of hypocalcaemia and potentially seizures.

• blunt trauma to a peripheral nerve (eg. local ischaemia, prolonged pressure, acute compression or stretching) may cause a neuropraxia in the anatomic area that the nerve supplies which usually also involves muscles and paralysis, the duration of which depends on the severity of the injury, and may resolve within minutes or months.
  • common examples include:
    • greater occipital nerve
      • often a trigger area for migraine
      • causes pain over occipital and vertex of scalp
    • lesser occipital nerve
      • supplies parietal area of scalp and peri-auricular areas and can cause pain from base of skull and allodynia of parietal scalp and ear
    • nervus intermedius neuralgia
      • can cause paroxysms of severe, sharp, shooting pain centered deep within the ear canal that frequently radiates to the adjacent scalp and parietotemporal region on the same side
      • usually as a postherpetic neuralgia
      • can be injured or irritated at either:
        • cisternal course:
          • emerges from the brainstem in the cerebellopontine angle, it sits tightly between the main motor root of the facial nerve (CN VII) and the vestibulocochlear nerve (CN VIII)
          • most commonly by aberrance of the anterior inferior cerebellar artery (AICA) or, less frequently, the posterior inferior cerebellar artery (PICA) and vertebral artery or by ass lesions in the cerebellopontine angle, such as acoustic neuromas (vestibular schwannomas) or meningiomas
        • at the internal auditory meatus (canalicular segment)
          • fractures of the temporal bone, localized inflammation or operative injury
    • radial nerve palsy
      • eg. in the intoxicated patient sleeping on a chair
      • results also in wrist drop
    • ulnar nerve symptoms
      • from repeated stretching or compression of the nerve around the elbow
      • usually pain at elbow and numbness 4th/5th fingers
    • carpal tunnel syndrome
      • causing median nerve symptoms numbness 1st-3rd fingers, pain hand which may be referred proximally up the arm
    • Morton's digital neuroma of the foot
      • causing pain in the forefoot (metatarsalgia) and numbness of 3rd/4th toes
    • meralgia paresthetica
      • cutaneous branch of lateral femoral nerve compressed near the inguinal ligament
      • causes numbness and pain of groin and lateral thigh
    • notalgia paresthetica
      • posterior rami nerves
      • numbness and often pruritus in area of infrascapular skin which is difficult to reach with the patient's hand
      • mainly adults aged > 40yrs with cervical spine issues
      • see emedicine
    • cheiralgia paresthetica
      • superficial branch of radial nerve
      • numbness at anatomic snuffbox which may extend dorsally over back of hand, thumb and index finger
      • usually due to pressure from wristband, bracelet or handcuffs
    • brachialgia paresthetica nocturna
      • sensory branch of median nerve
      • perhaps due to prolonged wrist flexion whilst sleeping
    • gonyalgia paresthetica
      • infrapatellar branch of saphenous nerve
      • causes numbness and pain on inframedial aspect of knee and is often bilateral due to compression of the nerve by the knees
    • obturator nerve
    • posterior tibial nerve
    • herpes zoster (shingles)
    • other compartment syndromes such as peroneal or anterior compartment lower leg following oedema or bleeding from muscle injury or fractures
• lacerations and other sharp injuries including iatrogenic from injections or scalpel may cause more permanent loss of sensation
• other rare causes include neoplastic infiltration of nerves, leprosy and diphtheria

• numbness down one side of the body involving side of face and same side arm or side of face, same side arm and leg is highly suggestive of a CNS problem such as a transient ischaemic attack (TIA) or stroke (CVA), migraine, or rarely, a spinal cord syndrome

• bilateral ascending numbness +/- pain/weakness mainly affecting the lower legs and possibly hands - the further from the spinal cord, the greater the severity, suggests a subacute or chronic metabolic cause, but could be caused by poor circulation as in Raynaud's, exposure to cold, hypotension or a proximal circulatory insufficiency involving both legs.
• see peripheral neuropathy

• suggests the possibility of limb ischaemia due to arterial embolus or insufficiency, or a compartment syndrome.

• suggests a nerve root or spinal cord aetiology, or perhaps herpes zoster (shingles)
• eg. lower leg numbness associated with lumbar disc prolapse and sciatica

• loss of pain and temperature but preservation of other sensation

• central cord lesion affecting the crossing fibres (eg. syringomyelia)
• cord hemisection (Brown-Sequard)
  • eg. compression or intramedullary neoplasm
  • features:
    • LMN lesion at level of lesion
    • UMN lesion below level of lesion
    • ipsilateral loss of position, vibration and touch
    • contralateral loss of pain an temperature
  • see Spinal cord syndromes and lesions
• lesions of lateral medulla
  • eg. post-inf. cerebellar thrombosis
  • eg. syringobulbia

• neurology involving multiple unrelated peripheral nerves
• usually due to vasculitis