Background/Purpose:   ACDC is a hereditary ectopic
mineralization syndrome caused by mutations in the NT5E gene that encodes
CD73.  CD73 is a membrane bound 5′ ecto-nucleotidase that hydrolyzes 5’AMP into
adenosine and inorganic phosphate.  This autosomal recessive disease clinically
manifests with extensive mineralization of arteries predominantly of the lower
extremities.  Claudication and arthralgia complaints are prominent among
affected individuals.  The anatomic distribution of some of the calcifications
in ACDC could be due to a tissue-specific differential of adenosine receptor
levels on different cell types, which could apply to not just vessels but the
joint capsule as well.  The focus of our study is to characterize the rheumatic
manifestations of patients with ACDC.

Methods:   Six individuals with
genetically confirmed disease where assessed clinically, radiologically, immunologically
and biochemically.  Demographics and complete history and physicals were
catalogued.

Results:    Four out of 6 patients were
female (Table 1).  The mean age at onset of symptoms was 16.7 years.  In 5 out
of 6 individuals, the initial clinical presentation was arthralgia/arthritis
and hence the first specialist seen was a rheumatologist.  In the 6th instance,
the initial presenting complaint was claudication hence culminating in
evaluation by a vascular surgeon.  The most common pattern of arthritis was a
symmetric, additive, small joint arthritis that in most cases was diagnosed as
rheumatoid arthritis at initial presentation.  The most common joints affected
included PIPs and MCPs including reports of pain, stiffness, swelling and
erythema.  Episodic flares lasting up to ten days were reported by all subjects
and these were responsive to either NSAIDs or short-term corticosteroids.  Plain
radiography demonstrates joint space loss, capsular calcification, heterotopic
bone formation, homogeneous areas of soft tissue calcification and degenerative
changes reminiscent of erosive osteoarthritis (image 1).  Carpal erosions and
meniscal calcifications were not a feature of the disease.  All patients were
ANA negative.

Conclusion:   This is the first study to
characterize the rheumatic manifestations of ACDC patients.  A mixed
degenerative-erosive radiological pattern is highlighted.  Rheumatologists may
be the first specialists to encounter these individuals and the presenting
symptoms may be confused with rheumatoid arthritis. 

Table 1. Clinical
characteristics of the patients

Figure
1. Moderate degenerative changes of distal third DIP with subluxation
and swan-neck deformity