- Clinical science
Neuralgic amyotrophy (also referred to as brachial neuritis or Parsonage-Turner syndrome) is a self-limiting inflammatory disorder of the brachial plexus, that mainly affects males between 20–30 years of age. There are two clinically similar, yet etiologically distinct forms of neuralgic amyotrophy (NA). Idiopathic NA is more common, often unilateral, and non-recurrent. It is thought to be an immune-mediated process triggered by preceding viral infection, immunization, or trauma. Hereditary NA is a rare, autosomal dominant condition that often affects both shoulders and is characterized by recurrent symptoms. In both types, patients present with acute onset of excruciating shoulder pain that lasts for weeks followed by patchy lower motor neuron paresis of the proximal muscles in the affected arm. Diagnosis is clinical, with nerve conduction studies and needle electromyography performed to identify which nerves are affected. Treatment is mainly supportive and involves analgesia and physical therapy. Most patients recover complete muscle strength within 2 years.
- Incidence: 1–3 cases per 100,000 population per year
- Peak age: 20–30 years
- Sex: ♂ > ♀
Epidemiological data refers to the US, unless otherwise specified.
- Idiopathic NA (more common)
- Autosomal dominant
- SEPT9 genetic mutation
The exact pathophysiology is unknown, but it is believed to be multifactorial.
- Environmental factors (e.g., viral infection, immunization, surgery) → activation of the immune system
- Mechanical factors (e.g., repetitive strain, recent strenuous exercise) → repeated stretching of the brachial plexus nerves → predisposition of the brachial plexus to immune-mediated injury
A combination of the above factors → patchy inflammation of the brachial plexus → axonal injury of the affected nerves → severe burning pain, followed by paresis of the muscles supplied by the affected nerve
- Acute phase
- Chronic phase
Progressive weakness and atrophy of the shoulder/arm muscles
- Occurs ∼ 2 weeks after the acute onset of pain
- Patchy involvement of more than one nerve of the brachial plexus
- Different degrees of lower motor neuron paresis of muscles innervated by the same peripheral nerve
- Nerves commonly affected:
- Suprascapular nerve; → paresis of supraspinatus, infraspinatus → weak abduction and external rotation of the shoulder; wasting of the supraspinatus and infraspinatus
- Long thoracic nerve → paresis of serratus anterior → winging of the scapula
- Axillary nerve; → paresis of deltoid → weak abduction of the arm
- Subscapular nerve; → paresis of subscapularis, teres major → weak internal rotation of the shoulder
- Phrenic nerve (rare) → paresis of hemidiaphragm → dyspnea
- Sensory loss: hypoesthesia: (numbness); paresthesia or dysesthesia (painful sensation to light touch) in the arm, forearm, and/or hand
- Autonomic dysfunction: edema, excessive sweating, faster growth of hair and nails on the affected limb
- Dysmorphism (e.g., hypotelorism, cleft palate, syndactyly): may be present in patients with hereditary NA
NA is mainly a clinical diagnosis.
Assessment of damage localization and severity
- Nerve conduction studies: show conduction block in the affected nerves
- Needle electromyography: show axonal degeneration; help differentiate between muscular and neural causes of weakness
- Exclusion of differential diagnoses
There is no specific causative treatment for NA. The condition is self-limiting and is treated symptomatically.
- Physical therapy
- Surgery: nerve grafts or tendon transfers are possible; only considered in protracted disease courses (> 2 years)
- Experimental therapies: glucocorticoids, immunotherapy, acupuncture, transcutaneous electrical nerve stimulation
- Prognosis is variable
- Idiopathic NA: often non-recurrent
- Hereditary NA: ∼ 75% of patients will have recurrent NA