Neuralgic amyotrophy: a long term follow-up of four cases.
Neuralgic amyotrophy or brachial plexus neuralgia is a condition of uncertain etiology. It needs to be differentiated from the usual brachial plexus injuries. Nerves outside the plexus especially the spinal accessory nerve are involved. Neuralgia is also a feature. Four cases were followed-up in detail over a period of two years. The condition usually resolves almost completely on its own.
Neurologic amyotrophy, a relative rare condition needs to be differentiated from the usual brachial plexus neuralgia especially since the mode of management of both are completely different. We followed up 4 cases of different aetiologies for 2 years and the same form the basis of this paper.
Four patients were referred to us the O.P.D.; one was referred for a post-traumatic brachial plexus lesion, one for post-injection nerve damage, and two for poliomyelitis. All patients were subjected to a detailed orthopaedic and neurological examination. The signs used to differentiate from polio, brachial plexus lesions and other causes of shoulder pain, were:
a) deep, dull, and vague, pain in the shoulder region,
b) sensory loss, especially in the axillary nerve distribution area,
c) motor weakness, not fitting into any known brachial plexus pattern, involving the trapezius (spinal accessory).
All patients were subjected to electromyographic (E.M.G.) and nerve conduction studies every three months. The follow-up was done fortnightly. The patients were followed up till they showed 80% motor recovery, as the pain and sensory deficit were relieved much earlier as compared to the motor deficit.
Patients were in the age group 10 to 25yr. All had shoulder pain, though some had involvement of the elbow or the neck. Deltoid and trapezius were most commonly involved. Sensory loss or deficit was seen in three of the cases mainly in the regimental badge area in the distribution of the axillary nerve.
All patients had sensory recovery and pain relief within 2-3 months. Ninety per cent motor recovery was seen within periods ranging from 1.5 to 2.5 years. Larger muscles recovered earlier than smaller muscles i.e. deltoid and trapezius before supra-and infra spinati and serratus.
The results were tabulated as given in [Table - 1].
Neuralgic arnyotrophy (syn. brachial plexus neuropathy, brachial plexus neuralgia, brachial plexus neuritis, Parsonage-Turner syndrome) is quite well described in neurological publications, but has only a few mentions in orthopaedic literature.
In 1948 it was first described as the presentation with sudden onset of severe pain affecting the shoulder girdle, followed by rapid development of weakness 2 and atrophy of the girdle musculature. Fasciculations are rare; cutaneous sensory distribution is common in the axillary (circumflex) nerve distribution.
It is important to know that even though most of the synonyms include the words 'brachial plexus', involvement of nerves outside the plexus is very common, especially the spinal accesory nerve. Thus trapezius weakness is an important differentiating feature to distinguish it from the commoner brachial plexus injury.
Although usually unheralded it can occur with or after viral infections, vaccinations, surgery and trauma, generally trivial. The exact aetiology is till now unknown, and it has been reported to have occurred in epidemics and in a familial pattern. Bilateral disease can be symmetrical or otherwise.
It has been postulated to be caused by an inflammatory process of infectious or allergic origin. It may even be several different diseases resulting in one syndrome.
E.M.G. studies are frequently used to confirm the diagnosis. The findings are i) abnormal sensory potentials, ii) lack of paraspinal denervation potentials, iii) abnormal conduction velocities.
These may indicate demyelination. It may also indicate a diffuse axonal damage; but focal lesions are never seen. Occasionally, even though the clinical findings are unilateral, the E.M.G. changes are bilateral. The prognosis is good with a functional recovery (of upto 90%) in 80% of patients at 2 years after onset and in 90% within 3 years of onset. More distal lesions recover faster than proximal ones. The upper plexus lesions recover faster than lower plexus ones.
Bacevich reported a patient with gleno-humeral subluxation. Foo and Swann showed isolated serratus anterior paralysis.
As for the treatment, though many have suggested a brachial plexus exploration and tendon transfers, these procedures are more suited for traumatic lesions; whereas for neuralgic amyotrophy a more conservative, masterly inactivity with exercises is better, as the disease is essentially self-limiting and self-recovering.
From an orthopaedician's point of view this entity is to be differentiated from brachial plexus lesions (as the prognosis is totally different) as well as from other sources of shoulder pain like a cervical disc prolapse or spondylosis.