Cerebrotendinous Xanthomatosis (CTX) Workup

Updated: Jul 07, 2017
  • Author: Robert D Steiner, MD; Chief Editor: Maria Descartes, MD  more...
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Workup

Laboratory Studies

LLaboratory studies in cerebrotendinous xanthomatosis (CTX) include various tests.

Whole blood, serum, and plasma studies

Findings reveal elevated plasma and serum cholestanol levels and low-to-normal cholesterol levels (usually 115-220 mg/dL). The cholestanol level is typically 3-15 times higher than mean levels in unaffected individuals and can range from 1.3-15 mg/dL. [20] The cholesterol-to-cholestanol ratio is said to be a better indicator of disease than cholestanol concentration alone. [46] A low cholesterol-to-cholestanol ratio in the diagnostic range is diagnostic in the appropriate clinical setting; however, additional confirmatory testing is recommended if feasible.

Low-density lipoprotein and triglyceride levels are also usually normal. High-density lipoprotein and very-low density lipoprotein levels vary. Although not typically obtained, bile acid intermediate and other sterol levels are also elevated, such as 7-dehydrocholesterol, [47] 7-alpha-hydroxycholesterol, and lathosterol levels. Some serum bile acid levels themselves are low. Measurement of 7-alpha-hydroxy-4-cholesten-3-one facilitates rapid, convenient diagnostic testing for cerebrotendinous xanthomatosis and may or may not be useful in monitoring treatment response. [48, 49] Measurement of the bile acid precursor (7-alpha, 12-alpha-dihydroxy-4-cholesten-3-one) enables sensitive dried bloodspot testing for cerebrotendinous xanthomatosis, possibly even newborn dried bloodspot testing. [50]

Urine studies

Urine testing of bile alcohols (typically pentols) using fast ion bombardment–mass spectroscopy has been performed after a positive serum cholestanol result. [51, 52] Current studies are exploring the use of tandem mass spectrometry as an efficient and affordable way to screen infants; however, no newborn screening has been implemented. [50]

Bile analysis

A large amount of cholestanol is present in the bile of affected individuals (4-11% vs < 1% in controls). [53, 54] As expected, a low concentration of chenodeoxycholic acid (CDCA) is observed along with high concentrations of bile alcohols (conjugated with glucuronic acid).

Cerebrospinal fluid (CSF) studies

Salen et al have reported an increased cholesterol-to-cholestanol ratio (1.5-20 times the reference range); however, this is not routinely analyzed for diagnostic purposes. [55]

Mutation studies

Once disease has been biochemically confirmed, mutation analysis is recommended.

Electrophysiology studies

Decreased nerve conduction velocities as well as somatosensory, motor, brainstem, and visual evoked potentials all relate to peripheral neuropathy. [56, 57] These often correct with CDCA therapy.

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Imaging Studies

Typical findings on MRI and CT scanning include diffuse atrophy of the brain, as well as focal lesions (including demyelinating lesions and, rarely, xanthomata) in the cerebellum, basal ganglia, and cerebrum. Typical patterns on brain MRI include bilateral lesions consistent with a metabolic abnormality. T2 hyperintensity of the dentate nuclei are characteristic of cerebrotendinous xanthomatosis and were present in 79% of patients in one study. [58] T2 abnormalities are also found in the globus pallidus, substantia nigra, and inferior olives with extension into the surrounding white matter in later years of the disease. Some hypointensity in the dentate nuclei was related to hemosiderin and calcification and was found on autopsy. Cerebrotendinous xanthomatosis should be considered in the differential diagnosis of leukodystrophies. [59]

Brain MRI fluid attenuation inversion recovery (FLAIR) sequences in one patient revealed cortical and subcortical hyperintensities in the temporal lobes) and globus pallidus. T2-weighted MRI revealed cerebellar hyperintensities within the dentate nucleus. Hypointensities were seen on T1-weighted and susceptibility MRI scans within the cerebellum at the level of the midbrain. [58]

Magnetic resonance spectroscopy reveals diffuse mitochondrial dysfunction and axonal damage, with large amounts of lactate and decreased N -acetylaspartate in the periventricular white matter and cerebellar hemispheres. [58]

Isolated spinal cord white matter disease has been described. [60, 61] MRI may reveal increased intensity in the lateral and dorsal columns, even in mainly cerebral forms of the disease. [58] Magnetization transfer imaging has been found to be a reliable quantitative indicator of the extent of damage in the brain parenchyma. [61] MRI can also be used to evaluate possible tendon xanthomata outside the central nervous system; enlargement of the tendons is evident in such cases.

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Other Tests

Other studies include electrophysiologic testing, prenatal testing (only performed if a family member is affected), and population-wide newborn screening (not yet implemented). [62, 63] Electrophysiological testing may reveal motor or sensorimotor peripheral neuropathy (demyelinating, axonal, or mixed). Somatosensory evoked potentials (SSEPs) are commonly affected. Delayed brainstem auditory evoked potentials are common, and visual evoked potentials are often abnormal. [64]

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Histologic Findings

CNS findings

Xanthomas and granulomas are found in multiple areas of the brain, including the cerebellar hemispheres, cerebellar peduncles, and globus pallidus. Further studies have reported more involvement of gray matter and have also described pathognomonic lesions of spindle-shaped lipid crystal clefts, fibrosis, and hemosiderin deposition in the dentate nucleus. [65] Neuropathologic findings described include lipid crystal clefts, neuronal loss, demyelination, reactive astrocytosis, and perivascular macrophages, suggesting the limited reversibility of the disease and poor prognosis if treatment is not started early.

Peripheral nerve findings

“Onion bulbs” have been described; this suggests that the process is chronic and demyelinating. Demyelination, remyelination, and primary axonal degeneration have been reported. Whether or not the process is a primary neuroaxonal process is unclear.

Muscular findings

Atrophy and pyknotic nuclei have been reported. Mitochondrial dysfunction has also been noted, as revealed by decreased respiratory chain activity and increased levels of pyruvate and lactate in the serum and cerebrospinal fluid. [35]

Liver findings

Typical findings include amorphous pigment and crystalloid forms associated with smooth endoplasmic reticulum, with some free-floating in the cytoplasm. [53]

Xanthomas

Birefringent crystals are surrounded by giant cells with foamy cytoplasm.

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