Arachnodactyly--a key to diagnosing heritable disorders of connective tissue.

Arachnodactyly literally means spidery fingers, and describes the long, slender fingers typical of patients with Marfan syndrome (MFS). Many clinicians regard arachnodactyly as pathognomonic of MFS; however, this view is misleading as arachnodactyly is a key element of the marfanoid habitus, which is present in several heritable disorders of connective tissue (HDCTs). Other features of the marfanoid habitus include long hands and feet, increased skin stretch, joint hypermobility and characteristic changes in the physiology of the pectum. Here, we focus on the differential diagnosis of diseases with features of the marfanoid habitus. Ectopia lentis (lens dislocation) and aortic root dilation or dissection are cardinal features of MFS. Distinguishing MFS from other HCDTs has important implications for treatment, as cardiovascular and ocular complications commonly seen in patients with MFS are not seen in all HDCTs. Joint hypermobility syndrome and Ehlers-Danlos syndrome are also HDCTs, neither of which is associated with ectopia lentis or aortic changes. Some of the rarer forms of Ehlers-Danlos syndrome are associated with severe vascular, dental and skin pathologies. This Review serves as a guide for correctly diagnosing members of the HDCT family.