The Ehlers-Danlos syndrome (EDS) is a heterogeneous group of disorders of collagen metabolism which manifest through a wide variety of symptoms. The cardinal features include joint hypermobility, as well as skin hyperextensibility and fragility. This is a rare disease, which occurs in 1:5000 individuals. It is divided into six subtypes according to the Villefranche classification with the classical, hypermobile, and vascular types being the most common. The genetic basis for these disorders are quite diverse, and in some instances, the exact genetic mutation is unknown. Where the mutation is known, it usually involves dysfunction in either the formation or crosslinking of collagen fibrils.

As the principle manifestation of this disease is joint hypermobility, the Beighton scale is used to assess the degree of hypermobility. As patients grow older, there is a tendency for flexibility to decrease; however, for children, generally a score of at least 5 out of 9 is considered diagnostic. Another characteristic of the disease is that patients frequently complain of joint pain and are prone to injuries such as joint subluxation and torn ligaments and tendons. Cutaneous manifestations such as marked skin hyperextensibility, widened atrophic cutaneous scars, and easy bruising with skin staining due to hemosiderin deposits are also prevalent. Furthermore, subcutaneous spheroids and molluscoid pseudotumors with scars over the knees and elbows can also be seen. Due to the connective tissue abnormality, children with these disorders can experience problems with motor development, muscle weakness and proprioception. Additionally, patients may be more prone to developing functional somatic syndromes such as fibromyalgia, chronic fatigue syndrome, irritable bowel syndrome and orthostatic intolerance to name a few.

Association between Chiari malformation and EDS

The association between Chiari malformation type I and connective tissue disorders (CTD) was initially described by Milhorat et al in 2007. In their cohort of patients, family history data appeared to show a relationship between CMI and CTD. They observed that a subset of Chiari patients who also had CTD appeared to have what they referred to as functional cranial settling. This was manifested by a reducible increase in the basion-dens interval and posterior gliding of the occipital condyles. This led to the conclusion that these patients suffer from occipitoatlantoaxial hypermobility, which is responsible for the treatment failure from decompression surgery in these patients. As a result, a belief that these patients require occipito-cervical fusion operations in order to achieve symptomatic relief has been developed. Although their manuscript illustrated the dynamic changes which occur in patients with occipitoatlantoaxial hypermobility with the use of vertical or sitting MRI, further studies have not demonstrated the utility of upright MRI. Henderson has described the potential harmful effects of this type of cranial settling. In a finite analysis model, when the clivo-axial angle is less than 125 degrees, the forward angulation produces a distracting force on the neural elements, which can result in neurologic dysfunction. Other authors sought to elucidate which patients would benefit from a decompression alone and which patients would progress to treatment failure if their surgical intervention did not include an occipital-cervical fusion. Brockmeyer et al. determined that a subgroup of “complex” pediatric Chiari malformation patients exist that indeed have a higher rate of requiring occipital-cervical fusion. These patients include those that present with basilar invagination, Chiari malformation 1.5 (tonsillar herniation along with brainstem herniation), and a clival-axial angle less than 125 degrees. Although it was initially thought that ventral brainstem compression, as defined by the pB-C2 line, is an independent predictor for treatment failure, further studies have not shown this to be the case. However, the pB-C2 line is still useful as a quantitative measure of ventral brainstem compression.

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