Purpose or Case Report: We report a case of 2-year-old female, twin, low birth weight (37 weeks, 1630 g - 3.59 lb), who was referred to our hospital to study an indurated nodular tumor involving her left leg, which extended from her pelvis to her left foot. Blood tests showed only an increase in alkaline phosphatase (862 mg/dl). Lower-limb X-ray was performed, which showed an extensive calcified mass with fibrillar pattern affecting dermis and deep connective tissue. MRI was also performed and showed an extensive signal alteration in muscle and dermis with hipointense signal in relation to heterotopic calcifications.
The differential diagnoses were Albright hereditary osteodystrophy (AHO), fibrodysplasia ossificans progressiva (FOP), and progressive osseous heteroplasia (POH).
AHO was ruled out because of the lack of compromise of muscle plane, and the absence of congenital malformations (such as brachydactyly, obesity, low height), hypocalcemia and hyperphosphatemia. Similarly, FOP was also ruled out since it is characterized by muscle ossification, with no dermal calcifications, and hallux malformation (also absent in this case).
The diagnosis reached was POH, which is a rare genetic (autosomal dominant inheritance) disorder characterized by progressive periarticular ossification of dermis and deep connective tissues (muscles, tendons and ligaments), with no congenital malformations. The diagnosis is built upon the clinical symptoms, imaging findings and genetic study (GNAS mutation). There is no effective treatment, with frequent progression to ankylosis.
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Conclusions: It is important for the pediatric radiologist to know about progressive osseous heteroplasia and its main differential diagnoses, and the importance of a simple x-ray study for the clinical suspicion and diagnosis of this infrequent entity.