Pain and neuromuscular diseases (facial paralysis)

PAIN is an unpleasant sensory/emotional experience associated with actual or potential tissue damage or described in terms of such damage

It is described by duration, site, distribution, type

1. Acute pain – sudden onset, obvious cause, identifiable pathology, responds to analgesics, and treatment of the pathology, associated with the emotions of fear and apprehension.

2. Chronic pain – insidious onset, no evident cause or readily identifiable pathology, responds poorly to analgesics, patient depressed

Physiology of pain:

  • Nociceptive stimuli (inflammation, infection, trauma, chemicals, thermal stimulus, biochemical stimulus)
  • Acts on peripheral pain receptors (non myelinated nerve fibres).
  • The impulse transmitted in form of a chemical transmitter substance across the synaptic cleft & an electric potential along the neuron.
  • Pain is perceived centrally causing peripheral release of endorphins (endogenous morphines)
  • From small interneurons that block the presynaptic release of the chemical pain transmitter (substance P) = tolerance

Gate control theory of pain:

  • Spinal gates at dorsal horn – at each segment of spinal cord
  • Heat, touch and pain impulse compete for the gate – therefore non painful stimulus blocks transmission of noxious stimulus
  • Modulated by substantia gelatinosa (SG) in the dorsal horn
  • Which then influences the first central transmission cells (T cells)
  • SG – modulating gate – permits only one type of impulse to pass through
  • Larger nerves eg. touch receptors carry impulse to brain quicker and get through gate, blocking nociceptors
  • Therefore use massage and heat therapy to inhibit pain sensation

Causes of facial pain and headaches

1. Local causes:

  • Dental or oral disease
  • Referred pain
  • Upper respiratory tract lesions
  • Neck lesions
  • Ocular lesions/ defective vision
  • Trauma

2. Neurologic causes:

  • Trigeminal neuralgia
  • Glossopharyngeal neuralgia
  • Herpetic neuralgia
  • Intracranial disease

3. Psychogenic causes:

  • Tension headaches
  • Atypical facial pain
  • Temporomandibular pain dysfunction syndrome

4. Vascular causes:

  • Migraine
  • Migranous neuralgia
  • Temporal arteritis

5. Systemic causes:

  • Severe hypertension
  • Drugs (vinca alkaloids etc)

Diagnostic features of conditions presenting with orofacial pain

Common diseases in this list need to be ruled out before diagnosis of rare conditions

1. Acute osteomyelitis:

  • Causative lesion – carious tooth/PDL disease, and bone swelling
  • Moth eaten appearance only manifests when approx 30% of bone undergoes osteolysis

2. Acute pulpitis:

  • Sensitivity to temperature extremes and sugary foods
  • ↑ pain at night or when lying down.
  • Vitalometry – indicates that the pulp is still vital
  • Percussion sensitivity – indicates apical spread

3. Apical abscess:

  • Non vital tooth with fistula, parulis or extra oral drainage tracts
  • This may be acute (with febrile presentation) or chronic

4. Cracked tooth syndrome:

  • Apico-occlusal crack which does not show up on x-ray
  • Pain on mastication
  • Lateral pressure on the inclines of the cusp causes pain

5. Cluster headaches:

  • Seasonal headaches with acute episodes in the evenings + ipsilateral conjunctival
    reddening and nasal discharge

6. Internal derangement of TMJ meniscus/ capsule adhesions

7. Myalgia of masticatory muscles:

  • Pain and spasm of muscles of mastication – marked by a trigger point on one or more of these muscles (masseter, medial and lateral pterygoids, temporalis)
  • Usually found in patients with a history of jaw clenching on anxiety

8. Otitis media:

  • Unilateral hearing impairment and bulging, perforated, red or purulent tympanic membrane

9. PDL abscess:

  • Expression of pus from the PDL pocket of a vital tooth
  • Characterized by presence of calculus and alveolar bone damage
  • If the tooth is non vital, it’s a perio-endo lesion

10. TMJ capsulitis/ synovitis/ arthritis:

  • Pain over the joint
  • Limited mouth opening or deviation on opening
  • Crepitus on palpation of the TMJ – indicates bone erosions – secondary to arthritis

11. Neuralgia (Trigeminal, Glossopharyngeal or Postherpetic):

  • Pain of neural origin, paroxysmal pain
  • Distinct trigger zone on skin/ in mouth
  • Middle aged or old patients, female patients
  • Trigeminal neuralgia is called ‘Tic Doloureux’ when it is accompanied by spasms of the muscles of facial expression

Classical trigeminal neuralgia:

  • Sudden unilateral, severe, brief, stabbing, recurrent pains in the distribution of trigeminal nerve branches
  • Pain is paroxymal
  • Provoked by light touch
  • Confined to trigeminal distribution
  • Unilateral
  • Lasts from few seconds to 2 minutes
  • Etiology: Intracranial compression of nerve by vasculature/foramina (osteopetrosis)
  • Diagnosis: History, CT scan, MRI, LA during an attack attenuates the pain instantly
  • Management: Carbamazepine, cryotherapy, vascular decompression

12. Atypical facial pain:

  • No known organic cause (diagnosis of exclusion)
  • Described by the patient in vague terms, treated as a symptom of depressive illness
  • It is also called psychogenic pain

13. Myofascial pain dysfunction syndrome (MPDS)

The diagnostic protocol for acute facial pain

Is the contributing lesion clinically visible (intra- and extra-oral examination for caries, PDL
disease, swellings, erosions, joint sounds, radiographic changes)?

− Is it accompanied by fever (a sign of acute disease)?

− Pulp or PDL: Abscess or osteomyelitis
− Mucosal lesions: Viral vesiculo-ulceration
− Facial swelling: Cellulitis or space infection
− Salivary swelling: Mumps or obstructive sialadenitis
− TMJ or mid ear: Infectious capsulitis or otitis media

If NO:

1. Dull or episodic aches:

Dull and episodic aches in jaws, TMJ and saliva

2. Constant ache:

  • Teeth or jaws:
    − Atypical facial pain
    − Myalgia of muscles of mastication
  • TMJ: Temporomandibular myalgia

3. Acute episodic ache:

  • Short term (seconds): Trigeminal neuralgia
  • Long term (minutes): Cluster headaches

NB: Manage pain and re-evaluate in 1 wk to eliminate an organic source eg cracked tooth

4. Chronic episodic ache:

  • Teeth or jaws:
    − Atypical facial pain
    − Myalgia of muscles of mastication
    − Cardiogenic (one of the signs of hypertension)
    − Vasogenic (migraine)
  • TMJ: Myalgia

Facial paralysis

UMN lesion: Lesion of the neural pathway above the anterior horn cell of spinal cord, or motor nuclei of the cranial nerves

LMN lesion: Affects nerve fibers traveling from anterior horn of spinal cord or cranial motor nuclei to the relevant muscles

Difference between upper and lower motor neuron lesions

1. Bell’s palsy: Picture

  • LMN paralysis of the face – due to inflammation in the stylomastoid canal
  • Reversible in 80% of cases
  • Management: Corticosteroid therapy

2. Ramsay Hunt syndrome:

  • Severe facial palsy – due to herpes zoster infection of the geniculate ganglion of the facial nerve
  • In hereditary craniofacial malformation

3. Tardive dyskinesia: Picture

  • Complication of longterm treatment with phenothiazines or butyrophenones
  • Clinical: Involuntary facial movements

4. Horner’s syndrome: Picture

  • A series of signs and symptoms – secondary to trauma to the cervical sympathetic trunk
  • Clinical: Miosis (papillary constriction), ptosis (drooping eyelids), facial anhidrosis (loss of sweating) and occasionally enophthalmos

5. Adie’s pupil: Unilateral dilatation + very slow light reflex – due to syphilis. Picture

6. Argyll-Robertson pupil: Picture

  • Failure of light reflex, but dilation for accommodation.
  • Also seen in neurosyphillis + other conditions affecting the Edinger Westphal nucleus eg diabetes mellitus, sarcoidosis, encephalopathies, midbrain tumors, trauma and amyloidosis

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