Parsonage-Turner syndrome

Parsonage-Turner syndrome, also known as neuralgic amyotrophy or idiopathic brachial plexitis, is an acute idiopathic and self-limited brachial neuritis.

Epidemiology

There is a male predominance (M:F 2-11.5:1) ¹. Patients from 3 months to 85 years old have been reported, but the majority are between the 3^rd to 7^th decades of life.

Clinical presentation

The presentation is typically quite sudden, with an onset of a painful shoulder girdle and progressive weakness. Symptoms are, however, non-specific and can mimic numerous other much more common conditions such as cervical spondylosis, labral tear with paralabral cyst and other suprascapular notch masses, rotator cuff deficiency, shoulder impingement, calcific tendonitis, and adhesive capsulitis ^1,2.

The findings are unilateral in two-thirds of cases. Bilateral involvement has been reported.

A combination of history, electromyography (EMG) (which demonstrates denervation changes, especially of the suprascapular nerve), and imaging make the diagnosis. 

Pathology

The etiology is uncertain, although a localized infectious (viral) or immunological process is suspected. Post-surgical cases, particularly after cervical decompression, have been described ⁵.

In almost all cases (97%) the suprascapular nerve is involved and is the only nerve involved in 50% of cases ². The axillary nerve and subscapular nerve are also sometimes involved, either in combination or alone. 

The most frequently involved muscles are supraspinatus and infraspinatus (innervated by the suprascapular nerve) followed by deltoid (innervated by the axillary nerve). 

Radiographic features

MRI

The most striking features on MRI are denervation changes in muscles. Initially, the muscle appears normal. Over the next few weeks, high T2 signal develops. Gradually, especially in patients with a protracted course, atrophy and fatty infiltration will develop with the increase in T1 signal and decreased muscle bulk. Also later in the course of the disease, muscle wasting without fatty infiltration may be evident.

MRI is chiefly useful in excluding other causes of shoulder pain and dysfunction, particularly compressive masses in the spinoglenoid notch.

Treatment and prognosis

The condition is typically self-limiting with supportive therapy only required. The pain first resolves. Weakness may persist for many years but usually resolves in 2 to 3 months (90% of patients will have an excellent recovery by 3 years) ².

History and etymology

This syndrome was first described in 1879 by French physician Alix Joffroy (1884-1908) ^6,7, however, was popularized with a larger series in 1948 by British neurologists Maurice John Parsonage (1915-2008) and John W Aldren Turner (1911-1980) ³.

Differential diagnosis

The differential diagnosis for the MRI findings includes ^1,2:

• disuse atrophy of shoulder girdle muscles

• quadrilateral space syndrome

• other entrapment syndromes around the shoulder

  • mass in the suprascapular notch (e.g. ganglion)

• trauma