Parsonage-Turner Syndrome (Neuralgic Amyotrophy)

Parsonage-Turner syndrome (neuralgic amyotrophy, idiopathic brachial plexus neuritis) is an immune-mediated disorder of the brachial plexus and its branches. It is defined by attacks of severe neuropathic upper-limb pain followed by patchy, multifocal weakness and atrophy.

Why it matters. It is the great mimic of the upper limb and is frequently misdiagnosed as a rotator cuff tear, a cervical radiculopathy or a simple compressive nerve entrapment. Recognising the painful-onset, patchy palsy prevents the misdiagnosis and the unnecessary operation that goes with it. Early recognition also allows pain control, rehabilitation and realistic counselling, because recovery takes months to years and is often incomplete.

How common. A prospective primary-care cohort found a one-year incidence of classic neuralgic amyotrophy of 1 per 1,000, suggesting the disorder is 30-50 times more common than previously thought (DOI). It has long been under-recognised, and awareness is the main barrier to diagnosis. Idiopathic disease has a slight male predominance.

A two-hit model. The proposed mechanism runs from a susceptible nervous system to a structural lesion in four steps:

1. Predisposition - a susceptible peripheral nervous system, clear in hereditary disease with SEPT9 mutations
2. Trigger - an immune-activating event, listed under the history below
3. Immune attack - focal inflammatory injury to specific nerves or fascicles within the brachial plexus
4. Fascicular constriction - swelling, then incomplete and complete hourglass constriction, and finally fascicular entwinement, a continuum seen on high-resolution ultrasound

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The constricted segment. Histology shows inflammatory cell infiltration, demyelination and a reduced number of nerve fibres.

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Idiopathic versus hereditary. The hereditary form is roughly ten times less common than the idiopathic form.

By nerve distribution. The disease has a predilection for the upper and middle trunk, and the long thoracic and suprascapular nerves are the ones most often hit. Distal mononeuropathies occur too, but the lesion still sits proximally in the parent nerve. A patchy distribution that crosses nerve and root territories is the hallmark.

Pain comes first. The attack opens with sudden, severe, neuropathic shoulder or arm pain that often wakes the patient. It lasts days to weeks, and the weakness emerges as it eases. This painful prodrome is the single most useful historical clue: a spontaneous upper-limb palsy with a preceding bout of disproportionate neuropathic pain is neuralgic amyotrophy until proven otherwise.

Triggers. Ask about each, because one is found in roughly half of cases:

• Infection - a viral illness, including hepatitis E
• Vaccination - reported after several vaccines
• Surgery - a recent operation or anaesthetic
• Pregnancy - peripartum attacks are well described
• Exercise - strenuous or unaccustomed exertion

The rest of the history. Sensory symptoms are present in most (around three-quarters) but are milder than the pain. Take a family history, since recurrent attacks suggest the hereditary form.

Patchy, not anatomical. Weakness does not respect a single nerve or root, and a patchy pattern (for example winging plus deltoid weakness) points away from a compressive lesion and towards neuralgic amyotrophy. Examine the whole upper limb, because the deficit is rarely where the pain is worst. Inspect for scapular winging and periscapular and deltoid wasting, which comes on rapidly in affected muscles. Sensory loss is variable and often patchy, and reflexes are usually preserved unless a major nerve is affected.

Targeted motor testing. Four nerves deserve careful examination in any suspected case:

• Suprascapular - supraspinatus and infraspinatus weakness, with deep shoulder pain
• Long thoracic - serratus anterior weakness and medial scapular winging
• Anterior interosseous - FPL and FDP weakness, a weak OK sign, no sensory loss
• Posterior interosseous - finger extensor weakness, finger and thumb drop, wrist radial deviation

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The pain runs in three consecutive phases, and its character changes over time. Misreading the phase drives the wrong treatment.

Phase 1: neuropathic pain. The initial pain is intense and continuous, typically lasts around four weeks, and is out of proportion to any mechanical finding.

Phase 2: musculoskeletal pain. As the acute pain fades and weakness develops, especially periscapular weakness, a second, more musculoskeletal pain appears. It comes from altered scapular biomechanics, muscle imbalance and overuse of the compensating muscles, and it responds to scapular rehabilitation rather than to neuropathic drugs.

Phase 3: chronic intermittent pain. A longer-term pattern of intermittent neuropathic and exertional pain with fatigability follows. It is part of the residual burden that affects the majority at three years.

Why the phase matters. Phase 1 is treated with neuropathic analgesia and possibly early steroids; phases 2 and 3 with scapular and postural rehabilitation and pacing. Neuropathic drugs for the mechanical pain, or physiotherapy for the acute neuropathic pain, misfire. Persistent phase-1-type neuropathic pain alongside a structural constriction on imaging is what raises the question of surgery.

Diagnosis is clinical. History and examination carry the diagnosis: a painful onset followed by patchy upper-limb weakness with a typical nerve distribution. Investigations support and localise rather than confirm.

Electrodiagnostics. EMG and nerve conduction studies after about 2-3 weeks show patchy denervation in the affected muscles, with relatively preserved sensory studies in pure-motor branches. They help map the multifocal pattern and exclude radiculopathy.

High-resolution ultrasound. HRUS of the clinically affected nerves can show nerve swelling, incomplete or complete constriction, and fascicular entwinement. These form a continuum that may help predict recovery versus the need for surgery.

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MRI. MRI shows muscle denervation oedema as bright T2 signal. It is useful when the affected nerve is hard to pin down, or to exclude a structural plexus lesion.

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MR neurography. High-resolution MR neurography can localise the fascicular lesion itself.

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Bloods. No specific blood test confirms the diagnosis. Where relevant, test for an antecedent trigger: hepatitis E serology is worthwhile, as acute hepatitis E virus infection has a recognised association with neuralgic amyotrophy. A Swiss multicentre case-control study found a moderate association with neuralgic amyotrophy, but not with Guillain-Barre syndrome or Bell's palsy (DOI).

There is no proven disease-modifying drug, and treatment is largely supportive. The acute phase is dominated by pain, the recovery phase by weakness.

Pain control (days 0-14). The early pain is severe and a major source of distress, so analgesia is aggressive and multimodal. Neuropathic agents (for example gabapentinoids, amitriptyline) are combined with simple analgesia, and opioids may be needed short term.

Early corticosteroids (first month). Oral corticosteroids in the first month may shorten the painful phase and accelerate recovery in some patients. The evidence is weak and non-randomised, so discuss the uncertainty and risks before starting.

Protect and educate. Avoid overuse of the painful limb, protect it from traction injury, and explain the natural history early. Reassurance about the typical sequence, in which the pain settles and then weakness emerges, reduces anxiety.

Rehabilitation in the recovery phase. Rehabilitation is the mainstay once pain allows:

• Scapular stabilisation and periscapular strengthening
• Avoiding compensatory overload and glenohumeral stiffness
• Pacing and energy conservation for fatigability
• Addressing aberrant movement patterns, where a structured neuromuscular programme helps

Monitoring. Review the patient serially for re-innervation. Repeat EMG at 3-6 months if recovery stalls, and re-image with HRUS or MR neurography if a focal constriction is suspected and there is no recovery. Most spontaneous recovery occurs over months, but counsel that it can take 1-3 years.

When to consider surgery. Surgery targets the proximal intraneural lesion, not the classic distal entrapment site. The indications are:

• A discrete hourglass fascicular constriction on imaging with no recovery
• No clinical or electrical recovery by around 3-6 months
• A severe, persistent isolated mononeuropathy (for example AIN or PIN) amenable to neurolysis

The window is a range because the timing is uncertain: the Wang series recommends early surgery if there is no recovery by 3 months, but that comes from an operated population rather than a comparison of strategies.

Which operation. The options:

• Interfascicular neurolysis for a mild-to-moderate constriction
• Resection and neurorrhaphy (or grafting) for a severe constriction with loss of fascicle continuity
• Tendon transfers as salvage for established, non-recovering deficits (for example for serratus anterior or finger extension)

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A study of the clinical spectrum in 246 patients found that overall recovery is less favourable than usually assumed, with persisting pain and paresis in approximately two-thirds of patients followed for three years or more (DOI).

The phrenic nerve is the classic extra-plexal target, and its involvement is easily missed as "just deconditioning".

Presentation. Dyspnoea, especially orthopnoea (breathlessness lying flat), reduced exercise tolerance and disturbed sleep. These are often overshadowed by the shoulder pain and weakness, so the palsy is under-recognised.

Diagnosis. The diaphragm is assessed three ways:

• A raised hemidiaphragm on the chest radiograph
• Paradoxical diaphragm movement on the sniff test (fluoroscopy or ultrasound)
• Lung-function tests showing a fall in vital capacity from erect to supine; a supine drop of about 20% or more suggests diaphragm weakness

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Management. Most recover spontaneously over months to a couple of years, in line with the general natural history. Non-invasive ventilation for symptomatic or nocturnal hypoventilation bridges severe cases, and diaphragmatic plication is reserved for persistent, symptomatic unilateral palsy that fails to recover.

The spontaneous AIN or PIN palsy. Most spontaneous AIN and PIN palsies are now understood as forms of neuralgic amyotrophy with proximal fascicular constrictions. That reframes both diagnosis (image proximally) and surgery (operate proximally, if at all).

After surgery. Neuralgic amyotrophy can occur after any surgery or anaesthetic, sometimes in a limb remote from the operation. New patchy, painful weakness after an operation is not always a positioning or block injury.

The winging scapula. When serratus anterior winging follows a painful episode, neuralgic amyotrophy is the leading cause. Most recover, so nerve or tendon transfer is reserved for persistent, disabling winging after prolonged failure to recover.

Counselling. Set expectations early: the pain settles first, strength returns slowly over months to years, and recovery may be incomplete. Do not promise full recovery; honest counselling protects both patient and surgeon.

Global Epidemiology:

• Annual incidence around 1 per 1,000 in a prospective primary-care setting - far higher than older hospital-based estimates
• Long under-recognised; awareness is the main determinant of diagnosis rate worldwide
• Idiopathic form peaks around age 40; hereditary form (SEPT9) is roughly ten times less common with earlier, recurrent attacks
• Recognised triggers (infection including hepatitis E, vaccination, surgery, peripartum period, exertion) are identified in roughly half of cases

Side-by-Side Practice (no condition-specific registry exists for neuralgic amyotrophy):

There is broad agreement that the diagnosis is clinical, that most cases are observed first with supportive care, and that imaging (HRUS / MR neurography) is increasingly used to localise a proximal fascicular constriction and select the minority who may benefit from surgery.

Related pages: Cervical Radiculopathy for the compressive diagnosis this is most often mistaken for - the discriminator is that a radiculopathy follows one myotome while this is patchy across nerves; Scapular Winging and Long Thoracic Nerve Anatomy for the commonest single presentation, and Suprascapular Neuropathy for the nerve most often affected alongside it; Brachial Plexus Anatomy for the upper and middle trunk territory that accounts for 71% of cases; Anterior Interosseous Nerve Syndrome and Posterior Interosseous Syndrome for the distal phenotypes, where the lesion sits proximally in the parent nerve rather than at the classic entrapment point - which is why decompressing the usual site fails; Rotator Cuff Tears for the shoulder pathology that so often gets blamed and occasionally operated on before the diagnosis is made; Nerve Injury and Regeneration for why recovery is measured in months to years; Nerve Transfers for the reconstructive option when a constriction is diagnosed too late; and Thoracic Outlet Syndrome for the other non-compressive-looking cause of a painful upper limb.