Differential diagnosis: Quadrilateral Space Syndrome (QSS)
Article review of Hong et al., (2019)
Paper title and link to paper:
Quadrilateral space syndrome: The forgotten differential (Hong et al., 2019)
Overview of the paper:
The differential diagnosis of Quadrilateral Space Syndrome (QSS) was first brought to my attention by a case study presented by Jo Gibson via Clincal Edge. Here below I summarise another case study published in the Journal of Orthopaedic Surgery and bring together my learning on this area.
The paper by Hong et al., (2019) is a case study of a 48 year old male with a two month history of left shoulder pain. To summarise the patient initially presented with suspected rotator cuff pathology:
No trauma
No atrophy
Full passive range of movement
Normal X-ray
Painful active loss of abduction
Positive ‘impingement tests’
Two months following initiation of physiotherapy treatment and a CSI injection, his pain had reduced but he reported weakness around his shoulder. Mild atrophy of his deltoid was then noted on clinical assessment. An MRI was ordered. Muscle oedema and fatty infiltration was found in the deltoid as well as atrophy of the Teres Minor. Nerve conduction studies (NCS) suggested left axillary neuropathy and electromyography (EMG) showed active denervation potentials from the Deltoid and Teres Minor.
A diagnosis of Quadrilateral Space Syndrome (QSS) was made. An option of surgical decompression was suggested if his symptoms persisted or if he deteriorated. In the end, the patient continued to be treated conservatively. On his final follow up one year following the start of his symptoms, the patient reported nil pain during his work or ADLs. The weakness did however still persist.
This case highlights how QSS can mimic more common pathology in and around the shoulder. It is interesting to note though that even with a diagnosis a QSS, it did not really change management other than watchful waiting.
Overview of QSS:
The quadrilateral space, shown below, is a space in the posterolateral shoulder which is bordered by the Teres Minor superiorly, the Humerus laterally, the Teres Major inferiorly, and the long head of triceps medially. Within this space sits the axillary nerve and circumflex humeral artery. Supposed entrapment within this area, from sources such as a ganglion cyst to hypertrophied musculature is suggested to cause the condition known as QSS.
What are some features which may make us think of QSS as a differential diagnosis:
Presence of paraesthesia
Aggravated by flexion and external rotation
Muscle atrophy
Muscle weakness
What could we also look at? Maybe we could add in some simple objective tests to look at peripheral nerve testing. Jo Gibson talks about using the scratch collapse test around the axillary nerve. Alternatively, we can use simple tests set out by Annina Schmidt’s work on assessment of entrapment neuropathies. In the last year I have been using coins for hot and cold testing. Embarrassingly I have only just found out that the ‘cold coin’ is at room temperature and it does not need to be in the staff freezer to be cold…
Key take away points:
If symptoms are not progressing, does the next step really need to be a steroid injection or are we missing a more specific diagnosis such as QSS
Muscle weakness and/or atrophy may be due to denervation
As always, if anyone has any comments, further reading or suggestions on this topic please feel free to fire them at me on here or on my Twitter. I am always learning and any discrepancies on what I have written is thoroughly encouraged.