*3.2.1 Familial amyloid polyneuropathy (FAP)*

FAP is the most common neurological manifestation of fATTR. It is autosomal dominant, but the penetrance is variable and dependent on the type of mutation. If untreated, patients will have progressive neuropathy and disability resulting in death 10–15 years after disease onset [18]. The Val30Met mutation is the most common mutation associated with FAP, with a variable disease phenotype. Early onset disease (age < 50), which is more common in endemic regions of Japan and Portugal has a high penetrance and presents with a progressive polyneuropathy predominantly involving the small fiber nerves, which is typically manifested by loss of distal pain and temperature sensation, and progressive autonomic dysfunction; the latter includes orthostatic hypotension, neurogenic bladder, erectile dysfunction and impaired bowel function (malabsorption, diarrhea and constipation), and the presence of cardiac conduction blocks often necessitate pacemaker placement [10, 19]. On the other hand, late onset (>50 year old) phenotype, which occurs in non-endemic regions of Portugal, Sweden and Japan and sporadic cases in other parts of the world, is characterized by a low penetrance rate, male sex predominance. Late onset cases may not have significant clinical dysautonomia, and often present with a progressive distal neuropathy involving large and small fiber modalities, presenting with motor weakness and loss of vibratory and position sense early on, often with significant neuropathic pain. Autonomic dysfunction was the initial manifestation of 48% of early onset and 10% of late onset FAP in a previous study [20]. Late onset FAP is often misdiagnosed for more common entities in that age group such as idiopathic neuropathy

or chronic inflammatory demyelinating polyneuropathy (CIDP) partly because of lack of positive family history and autonomic symptoms [9, 19, 21]. Other reasons for misdiagnosis include presence of demyelinating features in the nerve conduction study, elevated cerebrospinal fluid (CSF) protein level [22, 23], and negative abdominal fat pad a nerve biopsy for Congo-red amyloid staining [9]. In a previous study on patients with familial amyloid cardiomyopathy, abdominal fat pad and bone marrow biopsy showed amyloid deposits in 67 and 41% of the patients respectively, while a sural nerve biopsy was positive in 83% of the patients who had that procedure [27]. It is therefore very important to do an amyloidosis workup, including echocardiography, nuclear imaging studies, and nerve biopsy on CIDP patients who do not respond to immunomodulatory treatment [9, 22, 23]. Val122Ile is the most common fATTR mutation in the USA, and usually has a cardiac phenotype, rather similar to ATTRwt (see below) [24, 25]; but carpal tunnel syndrome is rather common and neuropathy has also been reported in Val122Ile ATTR [26]. Unusual neuropathy phenotypes of FAP include upper extremity onset, ataxic and motor predominant [13]. For example, FAP associated with T60A mutation (which one of the more common mutations in UK) is characterized by a non-length dependent sensory loss and motor deficits, often rapidly progressive disease, and lack of positive sensory symptoms [17]. There is a diagnostic delay of up to 4 years for FAP diagnosis, especially when the autonomic symptoms are lacking [9, 21, 27]; As effective treatments are now available for FAP, it is very important to diagnose it in early stages, and before the cardiovascular and neurological disability are not severe. Presence of "red-flag" symptomatology have been emphasized to expedite the diagnosis, these include positive family history for neuropathy, unexplained heart disease including but not limited to atrial fibrillation, cardiac hypertrophy on echocardiography, carpal tunnel syndrome, gastrointestinal symptoms (anorexia, constipation, diarrhea, nausea, vomiting and unexplained weight loss, alternating constipation and diarrhea), renal involvement (proteinuria and renal failure) and ocular disease. The presence of >1 of the aforementioned features should prompt genetic testing for fATTR, as well as neurological and cardiovascular workup directed at the detection of amyloidosis [10, 28]. Gene sequencing has become increasingly affordable, and currently can be done free of charge for some patients in the USA (www.invitae.com/en/alnylam-act-hattr-amyloidosis; www.ambrygen.com/partners/hattr-compass/healthcare-provider). Another rather common diagnostic challenge is differentiating ATTR from primary (AL) amyloidosis. Monoclonal gammopathy of unclear significance (MGUS) has been reported in ~20–50% of patients with ATTR cardiomyopathy [29, 30]. Very high (>5.0) or low (<0.2) kappa/lambda ratio usually imply AL amyloidosis whereas normal ratio (0.7–1.2) suggests ATTR [31]. Sometimes, however, the result of kappa/lambda ratio is inconclusive. Immunohistochemistry (IHC), i.e. staining of amyloid deposits with antibodies to kappa and lambda light chains as well as TTR can be used to make the differentiation between AL amyloidosis and ATTR, however, amyloid subtype cannot be determined in 20–25% of cases with IHC alone [32]. Laser capture microdissection of amyloid deposits (microdissection done on Congo red stained tissue materials) followed by mass spectroscopy has increased the sensitivity and specificity of amyloid subtyping to 98–100% [32, 33] (**Figure 2**). Lipid chromatography-tandem mass spectrometry (LC-MS/MS) is another, more recent technology which determines the presence of mutant peptides with rather high accuracy [33–35]. However, LC-MS/MS had a sensitivity of 84% in picking up mutations that were detected in the genetic testing in a recent US study on 56 patients with fATTR cardiomyopathy [36]. Eight of the nine patients with mismatch between genetic testing and LC-MS/MS in the aforementioned study

**95**

*Neurological Manifestations of Transthyretin-Related Amyloidosis*

were African Americans, two of whom were homozygote to Val122Ile mutation. Sensitivity of LC-MS/MS to pick up mutations is diminished in instances that mutation does not result in significant mass shift, or is located in regions of the gene with short tryptic peptides [34, 37]. Nuclear imaging studies, using bone avid tracers 99mTc-DPD (technetium-3,3-diphosphono-1,2-propanodicarboxylic acid), 99mTc-PYP (technetium-pyrophosphate) and 99mTc-HMDP (technetium-hydroxymethylene diphosphonate) have been increasingly used to diagnose ATTR related cardiomyopathy as they are widely available, have good sensitivity and are not costly [38, 39]. Demonstration of cardiac uptake using the aforementioned methods in a patient with neuropathy and heart disease strongly suggests ATTR if AL amyloidosis is excluded using serum and urine immunoelectrophoresis/immunofixation and assessment of serum free light chains [29].

*Laser microdissection of amyloid deposits and mass spectroscopy. (a) Congo red-stained section of the postmortem heart specimen viewed under fluorescent light source. Bright red areas represent amyloid deposits. Areas microdissected for mass spectrometry-based proteomic analysis are indicated by purplecolored lines. (b) The results of mass spectrometry-based proteomics analysis of amyloid plaques obtained by microdissection. The identified proteins are listed according to the relative abundance they were represented in two independent microdissections. The top 10 proteins are shown. The columns show the protein name, the UnitProt identifier (protein accession number in the UniProt database, http://www.uniprot.org/), the molecular weight of the protein (MW) and two microdissections (S1-S2). The numbers indicate number of total peptide spectra identified for each protein. The most abundant protein is TTR. Apolipoprotein E, serum amyloid P-component and apolipoprotein A-IV are constituents of many amyloid types. In contrast, the peptides representing TTR (The top hit) are only seen in ATTR amyloidosis [from [91] with* 

Leptomeningeal and meningovascular amyloidosis, often with concomitant vitreous opacity, are rare neurological manifestations of fATTR. Leptomeningeal amyloidosis has been reported with different TTR mutations (Val30Met, Val30Gly,

Leu12Pro, Phe64Ser, Ala36Pro, Gly53Glu, Tyr69His, Ala25Thr, Tyr114Cys, Asp18Gly), sometimes in combination with FAP [40–47]. CNS symptoms include stroke, subarachnoid hemorrhage, dementia, hydrocephalus, ataxia, seizures, and sensorineural hearing loss. MRI studies may demonstrate leptomeningeal enhancement and superficial siderosis (sequela of intracranial bleedings) and there may be markedly elevated CSF protein [46, 48]. Ocular and meningovascular manifestations are specially common after liver transplantation, as the patient lives longer and mutant TTR is still being ecreted from the retinal cells and choroid plexus [49]. A previous study demonstrated that 27/87 (31%) of patients with Val30Met related FAP had focal neurological episodes, which occurred on average >14 years after the onset of FAP; more common after liver transplantation but also in patients with

*3.2.2 Familial leptomeningeal and oculomeningeal amyloidosis*

milder phenotypes which have a longer survival [47].

*DOI: http://dx.doi.org/10.5772/intechopen.84470*

**Figure 2.**

*permission].*

*Neurological Manifestations of Transthyretin-Related Amyloidosis DOI: http://dx.doi.org/10.5772/intechopen.84470*

#### **Figure 2.**

*Amyloid Diseases*

or chronic inflammatory demyelinating polyneuropathy (CIDP) partly because of lack of positive family history and autonomic symptoms [9, 19, 21]. Other reasons for misdiagnosis include presence of demyelinating features in the nerve conduction study, elevated cerebrospinal fluid (CSF) protein level [22, 23], and negative abdominal fat pad a nerve biopsy for Congo-red amyloid staining [9]. In a previous study on patients with familial amyloid cardiomyopathy, abdominal fat pad and bone marrow biopsy showed amyloid deposits in 67 and 41% of the patients respectively, while a sural nerve biopsy was positive in 83% of the patients who had that procedure [27]. It is therefore very important to do an amyloidosis workup, including echocardiography, nuclear imaging studies, and nerve biopsy on CIDP patients who do not respond to immunomodulatory treatment [9, 22, 23]. Val122Ile is the most common fATTR mutation in the USA, and usually has a cardiac phenotype, rather similar to ATTRwt (see below) [24, 25]; but carpal tunnel syndrome is rather common and neuropathy has also been reported in Val122Ile ATTR [26]. Unusual neuropathy phenotypes of FAP include upper extremity onset, ataxic and motor predominant [13]. For example, FAP associated with T60A mutation (which one of the more common mutations in UK) is characterized by a non-length dependent sensory loss and motor deficits, often rapidly progressive disease, and lack of positive sensory symptoms [17]. There is a diagnostic delay of up to 4 years for FAP diagnosis, especially when the autonomic symptoms are lacking [9, 21, 27]; As effective treatments are now available for FAP, it is very important to diagnose it in early stages, and before the cardiovascular and neurological disability are not severe. Presence of "red-flag" symptomatology have been emphasized to expedite the diagnosis, these include positive family history for neuropathy, unexplained heart disease including but not limited to atrial fibrillation, cardiac hypertrophy on echocardiography, carpal tunnel syndrome, gastrointestinal symptoms (anorexia, constipation, diarrhea, nausea, vomiting and unexplained weight loss, alternating constipation and diarrhea), renal involvement (proteinuria and renal failure) and ocular disease. The presence of >1 of the aforementioned features should prompt genetic testing for fATTR, as well as neurological and cardiovascular workup directed at the detection of amyloidosis [10, 28]. Gene sequencing has become increasingly affordable, and currently can be done free of charge for some patients in the USA (www.invitae.com/en/alnylam-act-hattr-amyloidosis; www.ambrygen.com/partners/hattr-compass/healthcare-provider). Another rather common diagnostic challenge is differentiating ATTR from primary (AL) amyloidosis. Monoclonal gammopathy of unclear significance (MGUS) has been reported in ~20–50% of patients with ATTR cardiomyopathy [29, 30]. Very high (>5.0) or low (<0.2) kappa/lambda ratio usually imply AL amyloidosis whereas normal ratio (0.7–1.2) suggests ATTR [31]. Sometimes, however, the result of kappa/lambda ratio is inconclusive. Immunohistochemistry (IHC), i.e. staining of amyloid deposits with antibodies to kappa and lambda light chains as well as TTR can be used to make the differentiation between AL amyloidosis and ATTR, however, amyloid subtype cannot be determined in 20–25% of cases with IHC alone [32]. Laser capture microdissection of amyloid deposits (microdissection done on Congo red stained tissue materials) followed by mass spectroscopy has increased the sensitivity and specificity of amyloid subtyping to 98–100% [32, 33] (**Figure 2**). Lipid chromatography-tandem mass spectrometry (LC-MS/MS) is another, more recent technology which determines the presence of mutant peptides with rather high accuracy [33–35]. However, LC-MS/MS had a sensitivity of 84% in picking up mutations that were detected in the genetic testing in a recent US study on 56 patients with fATTR cardiomyopathy [36]. Eight of the nine patients with mismatch between genetic testing and LC-MS/MS in the aforementioned study

**94**

*Laser microdissection of amyloid deposits and mass spectroscopy. (a) Congo red-stained section of the postmortem heart specimen viewed under fluorescent light source. Bright red areas represent amyloid deposits. Areas microdissected for mass spectrometry-based proteomic analysis are indicated by purplecolored lines. (b) The results of mass spectrometry-based proteomics analysis of amyloid plaques obtained by microdissection. The identified proteins are listed according to the relative abundance they were represented in two independent microdissections. The top 10 proteins are shown. The columns show the protein name, the UnitProt identifier (protein accession number in the UniProt database, http://www.uniprot.org/), the molecular weight of the protein (MW) and two microdissections (S1-S2). The numbers indicate number of total peptide spectra identified for each protein. The most abundant protein is TTR. Apolipoprotein E, serum amyloid P-component and apolipoprotein A-IV are constituents of many amyloid types. In contrast, the peptides representing TTR (The top hit) are only seen in ATTR amyloidosis [from [91] with permission].*

were African Americans, two of whom were homozygote to Val122Ile mutation. Sensitivity of LC-MS/MS to pick up mutations is diminished in instances that mutation does not result in significant mass shift, or is located in regions of the gene with short tryptic peptides [34, 37]. Nuclear imaging studies, using bone avid tracers 99mTc-DPD (technetium-3,3-diphosphono-1,2-propanodicarboxylic acid), 99mTc-PYP (technetium-pyrophosphate) and 99mTc-HMDP (technetium-hydroxymethylene diphosphonate) have been increasingly used to diagnose ATTR related cardiomyopathy as they are widely available, have good sensitivity and are not costly [38, 39]. Demonstration of cardiac uptake using the aforementioned methods in a patient with neuropathy and heart disease strongly suggests ATTR if AL amyloidosis is excluded using serum and urine immunoelectrophoresis/immunofixation and assessment of serum free light chains [29].

#### *3.2.2 Familial leptomeningeal and oculomeningeal amyloidosis*

Leptomeningeal and meningovascular amyloidosis, often with concomitant vitreous opacity, are rare neurological manifestations of fATTR. Leptomeningeal amyloidosis has been reported with different TTR mutations (Val30Met, Val30Gly, Leu12Pro, Phe64Ser, Ala36Pro, Gly53Glu, Tyr69His, Ala25Thr, Tyr114Cys, Asp18Gly), sometimes in combination with FAP [40–47]. CNS symptoms include stroke, subarachnoid hemorrhage, dementia, hydrocephalus, ataxia, seizures, and sensorineural hearing loss. MRI studies may demonstrate leptomeningeal enhancement and superficial siderosis (sequela of intracranial bleedings) and there may be markedly elevated CSF protein [46, 48]. Ocular and meningovascular manifestations are specially common after liver transplantation, as the patient lives longer and mutant TTR is still being ecreted from the retinal cells and choroid plexus [49]. A previous study demonstrated that 27/87 (31%) of patients with Val30Met related FAP had focal neurological episodes, which occurred on average >14 years after the onset of FAP; more common after liver transplantation but also in patients with milder phenotypes which have a longer survival [47].
