Symphalangism

► [Congenital fusion of one phalanx to another within the same digit]

Symphalangism results from failure of joint differentiation and should therefore be regarded as a type of synostosis (for a more detailed discussion on the terminology used for joint fixation, readers are referred to Chapter 8). Although the radiographic evidence of joint fixation may be lacking in infancy owing to the prevailing cartilaginous components, indirect signs such as hypoplasia of the joint and a distorted epiphysis unambiguously testify to the congenital defect of joint development. The anomaly is readily detected clinically, since no flexion occurs at the level of the affected joint and, as a consequence, the overlying skin lacks normal creases.

Symphalangism may occur as an anomaly predominantly involving the hands and/or feet (Tuncay et al. 2001), or as a symptom of a more generalized disorder. Familial symphalangism, a trait usually transmitted as an autosomal dominant, is distinguished into a proximal and a distal form, according to the level of joint involvement in the digits. However, associated proximal and distal symphalangism occasionally occur in the same family (Moumoumi et al. 1991). Proximal symphalangism (Cushing symphalangism, OMIM 185800), first described in a large American kindred (Cushing 1916), involves fixation of the proximal interphalangeal joints in the digits. The frequency of involvement decreases from the 5th to the 2nd digit, the thumb usually being spared. The distal interphalangeal joints in the feet may be affected. Carpal and tarsal fusion is also a feature (Spoendlin 1974). Conductive deafness attributable to ankylosis of the stapes at the oval window is commonly associated, suggesting that it may be related to an effect of the same gene (Strasburger et al. 1965; Gorlin et al. 1970). Absence of the 1st metacarpal, metacarpophalangeal synostosis, radial head dislocation, radiohumeral and humeroulnar synostosis, clubfoot, and accessory bones in the feet have been discordantly reported (Kassner et al. 1976; Wilder-vanck et al. 1967). Proximal symphalangism is caused by dominant mutations in the gene encoding Noggin and is therefore allelic to multiple synostoses syndrome (facio-audio-symphalangism syndrome, OMIM 186500), another autosomal dominant disorder with multiple progressive joint fusions as its principal feature (Gong et al. 1999; Polymeropoulos et al. 1995). Proximal symphalangism, carpal and tarsal fusion, hypoplasia or aplasia of various digital phalanges and corresponding nails, humeroradial synostosis with subluxation of the radial heads, cervical vertebrae fusion, and progressive conductive deafness are features in multiple synostoses syndrome (Fuhrmann et al. 1966; Maroteaux et al. 1972). Interestingly, bilateral stapedial ankylosis with hy-peropia, broad thumbs and great toes, and syndacty-ly in the absence of symphalangism occurs as a distinct entity (OMIM 184460) caused by mutation in the gene encoding Noggin - the same gene as causes symphalangism and multiple synostosis syndromes (Teunissen and Cremers 1990; Brown et al. 2002). Proximal symphalangism occurs among the multiple digital anomalies of the brachydactyly type C (OMIM 113100) and in association with diastrophic dysplasia (OMIM 222600) and Lenz-Majewski syndrome (OMIM 151050). Furthermore, proximal symphalangism has been described in association with multiple anomalies of hands and feet (OMIM 185750), including syndactyly, brachydactyly type D, clinodactyly, and hypoplasia of the thenar and hypothenar eminences (Learman et al. 1981).

Synostosis of the distal interphalangeal joints is referred to as distal symphalangism (OMIM 185700), a condition caused by a dominant mutation that is independent of that causing proximal symphalangism. The index finger is affected most typically, but reports of thumb and great toe involvement, with or without nail hypoplasia, have appeared in the literature (Matthews et al. 1987; Poush 1991). This anomaly may occasionally occur with Pfeiffer syndrome (acrocephalosyndactyly type V,OMIM 101600). Distal symphalangism has been described in several familial members over multiple generations in association with brachydactyly resembling type A1 brachydactyly, scoliosis, and clubfoot (brachydactyly-distal symphalangism syndrome, OMIM 113450) (Fig. 6.32) (Sillence 1978). Unlike those with brachy-dactyly type A1, affected individuals are tall. Additionally, distal symphalangism has been described in association with brachydactyly predominantly involving the distal digits (2nd fingers most involved), cone-shaped epiphyses, carpal anomalies, narrowing of the zygomatic arch, microdontia, and dental pulp stones (OMIM 606895) (Kantaputra et al. 2002). The hand anomalies are reminiscent of brachydactyly type B,but the absence of mutation in the ROR2 gene rules out this diagnosis. Distal symphalangism of the 5th fingers has been reported in the Char syndrome (OMIM 169100), a familial association of patent ductus arteriosus and unusual facies (high forehead, flat profile, downturned palpebral fissures, elongated nose with flattened nasal bridge, and thick lips), resulting from mutation in the transcription factor TFAP2B on chromosome 6p12-p21 (Char 1978; Sweeney et al. 2000). An abnormal 5th finger (clin-odactyly, absent middle phalanges with hypoplasia of the proximal and distal phalanges) is part of the clinical phenotype (Satoda et al. 1999).

A peculiar form of symphalangism is that in which synostosis occurs at the 1st metacarpophalangeal joint. This form is referred to as symphalangism Lewis type (OMIM 185650) from the name of a writer who was affected and - as he wrote of himself - could do nothing but writing because of his "extreme manual clumsiness" (Lewis 1955). Although somewhat misleading, use of the term sympha-langism is warranted here since the 1st metacarpal

Turner Syndrome Drumstick Phalanges
Fig. 6.32. Distal symphalangism in the same woman patient as depicted in Fig. 6.7. Observe synostosis in the distal interphalangeal joint of the 5th finger,associated with marked shortening of the middle phalanx

can be regarded as that homologous to the proximal phalanx in other digits. As discussed in more detail later in this chapter, metacarpophalangeal synostosis can occur with carpo/tarsal coalition, radial-head subluxation, and aplasia/hypoplasia of the middle phalanges (tarsal/carpal/digital synostoses, OMIM 186400). It is not certain, however, whether this is a separate entity, or the same disorder as 'multiple synostoses syndrome.'

Lenz Majewski Syndrome

Fig. 6.33. Juvenile rheumatoid arthritis in a 12-year-old girl with Turner syndrome in addition. Note severe joint space narrowing at the metacarpophalangeal and proximal inter-phalangeal joints of fingers 4 and 5, resulting in finger contracture. Moderate joint space loss of the carpus with soft tissue swelling is evident. Shortened 4th and 5th metacarpals and drumstick distal phalanges are consistent with Turner syndrome. (From Wihlborg et al. 2001)

Fig. 6.33. Juvenile rheumatoid arthritis in a 12-year-old girl with Turner syndrome in addition. Note severe joint space narrowing at the metacarpophalangeal and proximal inter-phalangeal joints of fingers 4 and 5, resulting in finger contracture. Moderate joint space loss of the carpus with soft tissue swelling is evident. Shortened 4th and 5th metacarpals and drumstick distal phalanges are consistent with Turner syndrome. (From Wihlborg et al. 2001)

The forms of symphalangism discussed above may be difficult to differentiate radiographically from several acquired causes of intra-articular anky-losis, including various arthritic (rheumatoid arthritis, seronegative spondyloarthropathies, septic arthritis) and connective tissue disorders (scleroder-ma, mixed connective tissue disease) (Fig. 6.33). However, a smooth osseous contour,in the absence of signs of joint destruction; a small lucent cleft possibly visible at the site of fusion; and hypoplasia of distal phalanges and proximal metacarpal heads may help identify symphalangism in equivocal cases. Occasionally, disorders involving soft tissue heterotopic calcification and secondary joint fixation mimic symphalangism: trauma, postsurgical scars, neurological injury, and thermal and electric burns belong in this category. Similarly, interphalangeal joint fixation or, less frequently, 1st metacarpophalangeal joint fixation occurs in fibrodysplasia ossificans progressiva (OMIM 135100), a connective tissue disorder characterized by bilateral short hallux; ossification of tendons, ligaments, and fasciae; and multiple joint ankylosis (Schroeder and Zasloff 1980).

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