To the Editors:

We read with great interest the article by Lambert and coworkers (1) regarding the high prevalence of enthesopathy of the shoulder in patients with ankylosing spondylitis (AS), as revealed by magnetic resonance imaging (MRI). Lambert et al evaluated the prevalence and characteristics of shoulder involvement in AS using clinical examination and MRI. As a result, they concluded that rotator cuff enthesopathy is a common lesion in AS, and that it is underrecognized by clinical examination. Moreover, the authors stated that intense acromial bone marrow edema (BME) at the deltoid enthesis (expression of enthesitis) is a hitherto undescribed and highly specific feature of AS (1).

In a previous study (2) we used ultrasonography to demonstrate that acromial enthesopathy of deltoid origin (described as deltoideal proximal insertion enthesitis [DPIE]) is a peculiar feature of spondylarthropathies (SpA) and, in particular, of psoriatic arthritis (PsA). Our study showed that the prevalence of DPIE in 100 consecutive patients with SpA and shoulder pain was 9%, but this prevalence increased to 17% in the subgroup of patients with PsA. DPIE was not observed in control patients (cohorts of consecutive patients with shoulder pain and rheumatoid arthritis, osteoarthritis, impingement syndrome, or fibromyalgia/localized myofascial pain). Using MRI, Lambert et al demonstrated acromial entheseal BME in 47% of symptomatic AS shoulders, and in only 1 control shoulder (in a patient with deltoid avulsion injury). These data confirm the high specificity of deltoideal acromial enthesopathy for SpA.

According to our results, the higher prevalence of deltoideal acromial enthesopathy observed by Lambert et al is probably attributable to the capability of MRI to detect entheseal BME (representing early expression of enthesitis) (3), even if higher sensibility of MRI with respect to ultrasonography in detecting enthesopathy is not confirmed in previous studies (4). However, the cohort of AS patients described by Lambert et al had a relatively long disease duration (2–29 years), whereas in our study DPIE was observed in patients with short disease duration (8–24 months). These data could partially explain the difference in the prevalence of deltoid enthesopathy.

Lambert et al showed deltoid enthesopathy associated with rotator cuff pathology, whereas in our study DPIE was seen as a unique lesion in half of the cases. This difference may be attributable to the different imaging techniques and the different disease durations of the patient cohorts. Lambert et al reported acromial BME in 8 of 17 AS shoulders (47%), of which 7 were described as having intense BME and 1 was described as having mild BME. Mild entheseal BME was also observed at the clavicular origin of the deltoid (2 of 17 AS shoulders). High signal, especially in T2 fat-suppressed and STIR sequences, was also seen in the deltoid muscle adjacent to its acromial origin in 4 of 7 shoulders. This last feature probably corresponds to the image obtained by ultrasonography (heterogeneous hypoechogenicity and thickening of the insertional tract of the deltoid on the acromion).

The accurate MRI descriptions by Lambert and coworkers and our ultrasonography observations lead to anatomic and physiopathologic considerations regarding enthesis and enthesitis in SpA. In fact, previous anatomic studies demonstrated that the deltoid arises from the superior surface and the lateral margin of the acromion with prominent tendinous origins, with rare interspersed muscle fibers, whereas deltoid muscle fibers are attached directly to the periosteum of the lateral third of the clavicle over its entire anterior surface (5). The acromial enthesis of the deltoid is, therefore, a fibrocartilaginous enthesis, whereas its clavicular enthesis is a fibrous one (6). In the study by Lambert et al, entheseal BME was observed especially at the acromial posterolateral margin and at the superior surface. In our study, DPIE and entheseal bone rearrangement were observed only at the lateral and superior aspects of acromion, but never in the anterior and clavicular portions of enthesis. Also, the distal diaphyseal insertion of deltoid on humerus is a fibrous enthesis, and this enthesopathy is characteristically unobserved in SpA (7, 8).

These observations support the hypothesis that fibrocartilage is the centrally involved anatomic structure in SpA enthesopathy (9). It is notable that in a single enthesis, with a different structure (both fibrous and fibrocartilaginous) in adjacent zones, inflammatory enthesitic changes are evident only in the entheseal zones rich in fibrocartilages. Further histologic and biochemical studies of deltoideal acromial enthesis could enrich our knowledge of SpA enthesopathy.

These observations lead us to state that the diagnosis and assessment of enthesopathy in SpA require an accurate knowledge of the entheseal anatomy and high-resolution imaging techniques (MRI and ultrasonography); enthesitis scoring methods based only on clinical or standard radiographic evaluation could lead to underdiagnosis or misdiagnosis of enthesitis (8). In fact, in our study, we noted that the clinical manifestations of this particular enthesopathy were always confused with those of an impingement syndrome, in the previous clinical examination. Only ultrasonography could differentiate between these 2 conditions (2). In the study by Lambert et al, the clinical examination, as defined by the Southampton physical examination schedule, did not include the possibility of deltoideal acromial enthesopathy (1).

In conclusion, we suggest that deltoideal acromial enthesopathy constitutes a hallmark of SpA, and not only of AS, that the diagnosis and assessment of acromial enthesopathy need high-resolution imaging techniques and deltoideal acromial enthesopathy should be added to clinical scoring methods for enthesitis in SpA.

  • 1
    Lambert RG, Dhillon SS, Jhangri GS, Sacks J, Sacks H, Wong B, et al. High prevalence of symptomatic enthesopathy of the shoulder in ankylosing spondylitis: deltoid origin involvement constitutes a hallmark of disease. Arthritis Rheum 2004; 51: 68190.
  • 2
    Falsetti P, Frediani B, Filippou G, Acciai C, Baldi F, Storri L, et al. Enthesitis of proximal insertion of the deltoid in the course of seronegative spondyloarthritis: an atypical enthesitis that can mime impingement syndrome. Scand J Rheumatol 2002; 31: 15862.
  • 3
    McGonagle D, Marzo-Ortega H, O'Connor P, Gibbon W, Pease C, Reece R, et al. The role of biomechanical factors and HLA–B27 in magnetic resonance imaging–determined bone changes in plantar fascia enthesopathy. Arthritis Rheum 2002; 46: 48993.
  • 4
    Kamel M, Eid H, Mansour R. Ultrasound detection of heel enthesitis: a comparison with magnetic resonance imaging. J Rheumatol 2003; 30: 7748.
  • 5
    Kumar VP, Satku K, Liu J, Shen Y. The anatomy of the anterior origin of the deltoid. J Bone Joint Surg Br 1997; 79: 6803.
  • 6
    Braun J, Khan MA, Sieper J. Enthesitis and ankylosis in spondyloarthropathy: what is the target of the immune response? Ann Rheum Dis 2000; 59: 98594.
  • 7
    Maksymowych WP. Ankylosing spondylitis: at the interface of bone and cartilage. J Rheumatol 2000; 27: 2295301.
  • 8
    Falsetti P, Frediani B, Acciai C, Filippou G, Galeazzi M, Marcolongo R. The role of ultrasonography of peripheral entheses in the diagnosis and assessment of spondyloarthropathies. Curr Rheumatol Rev 2005; (in press).
  • 9
    McGonagle D, Marzo-Ortega H, Benjamin M, Emery P. Report on the second international enthesitis workshop. Arthritis Rheum 2003; 48: 896905.

Paolo Falsetti MD, PhD*, Bruno Frediani MD*, Caterina Acciai MD*, Georgios Filippou MD*, Mauro Galeazzi MD*, Roberto Marcolongo MD*, * University of Siena, Siena, Italy.