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Rheumatology 2001; 40: 1320-1321
© 2001 British Society for Rheumatology
Letters to the Editor |
Acromioclavicular cyst and ‘porcupine shoulder’ in gout
Division of Rheumatology, Villa Pini Clinic, Chieti and
1 First Division of Internal Medicine, Spirito Santo Hospital, Pescara Hospital, Italy
SIR, We describe, for the first time, a gouty patient suffering from an acromioclavicular (AC) joint cyst containing urate crystals in whom an X-ray examination also revealed a spiny aspect of the left acromion. Among the radiographic pictures of gout and diffuse idiopathic skeletal hyperostosis (DISH), one of the most striking is the one identified (mainly in French and Italian populations) as ‘porcupine foot’ or ‘hirsute foot’ [1–3]. It features spiny bony outgrowths on the upper surface of the tarsus and can be seen better in the lateral view of standard radiographs. In gout, this new formation of bone is sometimes associated with erosive damage [2]. Our observation shows that gouty spiny alterations can also occur in other body areas.
In September 2000, we examined a left-handed 75-yr-old man with a history of recurrent attacks of gout involving mainly the knees, but also his left wrist and first metatarsophalangeal joints. Attacks had been treated with colchicine and/or NSAIDs. The patient had already been diagnosed as suffering from gout, based on the presence of urate crystals in synovial fluid samples. The patient had persistent high uric acid levels (>7.6 mg/dl). An adverse cutaneous reaction to allopurinol discouraged its administration, diffuse nephrolithiasis discouraged the use of uricosuric agents and changing the diet alone was unable to normalize the serum uric acid concentration. During the previous 3 months he reported the appearance of a small (2x2 cm), firm and moderately painful swelling overlying the left AC joint. Physical examination showed normal and painless motion of the left shoulder. Ultrasonography with a 7 MHz transducer revealed the cystic nature of the swelling and its communication with the AC joint. This examination also pointed to the existence of an initial conglomerate of urates in the cyst (Fig. 1A
). A subsequent examination of the synovial fluid aspirated from the cyst confirmed this possibility.
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Radiographs showed spiny bony outgrowths on the surface of the acromion (Fig. 1B
). Radiographic signs of DISH were absent in the spine, knees and feet. Extensive laboratory tests documented only elevated uric acid levels (8.7 mg/dl). The AC cyst has been described previously as a complication of the rotator cuff tear [4]. This disorder has been observed in an idiopathic form [5] but it has also been related to rheumatoid arthritis [6] and calcium pyrophosphate dihydrate crystal arthropathy [7]. In our patient, physical examination and ultrasonography showed no tear of the rotator cuff. Therefore, the AC cyst should be considered to be associated with a local inflammatory process.
Gout can involve many articular districts, mainly in the lower limbs, and it can produce several characteristic radiographic findings. Among these, the outgrowth of bony ‘thorns’ (sometimes associated with erosions) on the tarsus is called the ‘porcupine foot’. To our knowledge, this kind of picture has not been found previously in shoulder or in body areas other than the tarsus. Our present report confirms that the porcupine aspect is typical of gout but demonstrates that it can also involve areas other than the foot. We suggest that its presence in shoulder radiographs should be looked at as a possible indicator of gout. It would also be advisable to search for the porcupine shoulder condition in patients suffering from DISH, the other disorder related to porcupine foot.
Notes
Correspondence to: C. Palazzi, Via Legnago 23, 65123 Pescara, Italy. 
References
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- Craig EV. The acromioclavicular joint cyst. An unusual presentation of a rotator cuff tear. Clin Orthop1986;202:189–92.
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Cooper AM, Hayward C, Williams BD. Calcium pyrophosphate deposition disease involvement of the acromioclavicular joint with pseudocyst formation. Br J Rheumatol1993;32:248–50.
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