Genetically Established Familial Amyloidotic Polyneuropathy from India: Narrating the Diagnostic “Odyssey” and a Mini Review
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.294550
Source of Support: None, Conflict of Interest: None
Keywords: Chronic inflammatory demyelinating polyradiculoneuropathy, Congo red, familial amyloidotic polyneuropathy, porphyria, transthyretin gene
Amyloidosis associated with transthyretin gene (TTR) mutations is the commonest form of inherited amyloidosis. Human transthyretin is synthesized in the liver and to a smaller extent by the choroid plexus and retina. It transports thyroxine and retinol binding protein in physiological conditions. In the cerebrospinal fluid (CSF), it transports serum thyroxine across the blood brain barrier.,TTR is located on chromosome 18q12.1 and comprises four exons. About 120 different mutations have been reported, all within exons 2, 3, and 4. They are autosomal dominantly inherited with variable penetrance. TTR mutations cause a toxic gain of function: Transthyretin is destabilized and dissociated from its native tetramer, following which it misfolds and aggregates to form amyloid filaments that are deposited in various tissues and organs. The clinical spectrum includes familial amyloidotic polyneuropathy (FAP), familial amyloidotic cardiomyopathy (FAC), and familial leptomeningeal amyloidosis., FAP is the commonest phenotype, whereas leptomeningeal amyloidosis is uncommon. FAP was first reported from Portugal and subsequently from diverse ethnic populations. Phenotypic heterogeneity and overlap are increasingly recognized. There are a few reports of FAP from India and fewer have genetic confirmation.,, Because of its rarity as well as lack of focused clinico diagnostic approach, FAP in India may be misdiagnosed in the initial stages. We report the clinical, radiological, and histological features in genetically confirmed patients of Indian origin and highlight the diagnostic “odyssey.”
This study was carried out at the National Institute of Mental Health and Neurosciences (NIMHANS), Bangalore, India. Four patients were referred to a single neurology unit for the evaluation of neuropathic illness and eventually diagnosed to have FAP. Clinico demographic data including family history were gathered by direct face-to-face evaluation followed by a detailed examination. Nerve conduction study and MRI of brain and spinal cord were performed in all. Two patients (patients 1 and 4) underwent nerve biopsies at other centers. They were reviewed, fresh sections stained with Congo red, and examined under polarized microscope. Patient 3 underwent sural nerve biopsy at our center and sections were stained with hematoxylin–eosin, Masson's trichrome for collagen, Kulchitsky Pal for myelin, and Congo red for amyloid. All patients underwent skin biopsy at our center which was stained with hematoxylin–eosin and Congo red. Hepatic, renal, and thyroid function tests, ultrasound of abdomen and kidneys, echocardiogram, and electrocardiogram were carried out in all. The reasons for a delay in diagnosis were analyzed.
The cohort included four men. Symptom duration ranged from 1 to 10 years. The referral diagnosis, clinical features, and laboratory findings are summarized in [Table 1].
Patient 1(proband) developed progressive dysautonomia from 25 years of age and paroxysmal weakness of one or more limbs from 33 years of age [Figure 1]. Nerve biopsy was negative for vasculitis or amyloidosis. Between 33 and 35 years of age, he had two prolonged episodes of impaired consciousness. He had fluctuating blood pressure during the first episode and cardiac arrest during the second episode from which he was revived. He was diagnosed to have tubercular meningitis (TBM) based on brain MRI and CSF observations and referred for second opinion [Figure 1] and [Table 1]. His father had orthostatic hypotension, urinary incontinence, diarrhea and constipation, goiter, and Rombergism from 35 years of age and he died at 39 years of age. Review of his medical records showed that he underwent rectal biopsy, which did not reveal amyloidosis.
Examination of at our center revealed orthostatic hypotension, firm diffuse thyromegaly, anasarca, and ecchymotic patches over eyelids and trunk [Figure 2] and [Table 1]. No vitreous opacities were noted. There was diffuse hypotonia with bilateral foot drop and global areflexia. During the evaluation, he lapsed into altered sensorium with hypothermia and hypotension. Altered sensorium persisted despite normalization of blood pressure. Oxygen saturation, brain CT, scalp electroencephalogram, hepatic and renal function tests, and sodium levels were normal. His sensorium recovered over one week with supportive care and empirical treatment with intravenous methyl prednisolone.
Patient 2 (Brother of patient 1) manifested with dysautonomia, progressive cognitive decline, delusions, right-left confusion, aimless wandering, ataxia, and paroxysmal limb weakness [Figure 1]. His referral diagnosis was “TBM” based on the presence of leptomeningeal enhancement and elevated CSF protein. Examination at our center showed orthostatic hypotension, diffuse hypotonia with normal muscle power and stretch reflexes [Table 1].
Patients 1 and 2 had been analyzed for c. 2204 + 6TC mutation in IKBKAP at another center, which was negative. Both underwent abdominal fat pad biopsy at our center. Nerve biopsy of patient 1was retrieved and stained with Congo red. Characteristic amyloid deposits were noted both in skin and nerve [Figure 2].
Patient 3 presented with features of mononeuritis multiplex of one year and dysautonomia of eight months duration [Table 1]. Systemic complaints included episodic edema and erythematous rash over the anterior aspect of legs that used to respond to local steroid application and was considered to be “eczema.”His mother had an erythematous plaque, which had been diagnosed as “cutaneous amyloid”; further details were unavailable. Examination revealed distal dominant weakness, with median-innervated muscles of right and ulnar-innervated muscles of the left hand being preferentially affected. Bilateral foot drop was present. Knee and ankle stretch reflexes were absent. He was diagnosed to have chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) and advised immunosuppressive therapy. Biopsy of sural nerve and skin showed large deposits of amyloid. He died after 45 months of diagnosis while awaiting liver transplantation.
Patient 4 became symptomatic from 20 years of age, with episodic abdominal pain and vomiting, painless burns, progressive distal dominant weakness all four limbs, dysphagia, and weight loss (13% of body weight). He had been diagnosed to have “porphyria” and given a list of drugs to be avoided. Evaluation at our center revealed a moderately built and poorly nourished patient (body mass index: 13.3 kg/m2) with numerous thermal burns over the distal extremities and anterior abdominal wall with keloid formation [Figure 3]. Cranial nerves were normal. He had distal hypotonia, wasting and weakness, graded sensory loss to touch, pinprick and temperature over both lower limbs, anterior abdomen and upper limbs upto mid-arm, and hyporeflexia. Nerve and skin biopsy done at another center were reviewed and stained with Congo red, which confirmed the presence of amyloid deposits [Table 1].
We narrate the diagnostic “odyssey” of four patients with genetically confirmed FAP from India. Misdiagnosis of FAP is reported in 33% to 74%. In areas endemic for FAP like Portugal, diagnosis is quicker because of the high index of suspicion facilitated by a positive family history. On the other hand, sporadic occurrence, heterogeneous clinical manifestations, and reduced awareness among medical practitioners often pose a great challenge in areas with relatively low prevalence. Patients 1 and 2 (brothers) had been diagnosed to have familial dysautonomia, Shy–Drager syndrome, and spinocerebellar ataxia with seizures at different centers. In addition, the CNS involvement was mistaken for TBM. Patients 3 and 4 were diagnosed to have CIDP and 'porphyria' respectively. The diagnosis of FAP was not suspected by the referring clinicians and even when suspected, as in the case of patient 1, a perseverant search was not made. Other misdiagnosis reported in the literature include vasculitis, alcohol and paraneoplastic neuropathy, motor neuron disease, hereditary neuropathy with liability to pressure palsies, and lumbar canal stenosis among others.
TTR-associated amyloidosis affects multiple sites of neuraxis and multiple organs. Age at onset varies from third to the fifth decade. The cardinal manifestations are peripheral neuropathy and dysautonomia as seen in our patients. Features of dysautonomia include orthostatic hypotension, vomiting, diarrhoea alternating with constipation, neurogenic bladder, erectile dysfunction, abnormal sweating, anhidrosis, dry eyes, and dry mouth. Dysautonomia during the disease course occurs in 47% to 78% and is commoner in early-onset phenotypes. It seldom precedes neuropathy. Neuropathy is typically a progressive sensorimotor polyneuropathy. Four stages have been described with progression from sensory polyneuropathy (stage 1) to walking difficulty but independent ambulation (stage 2), walking with aids (stage 3), and chair-bound state (stage 4). Other patterns of neuropathy viz. small fiber neuropathy, multifocal neuropathy with predominant involvement of upper limbs, and ataxic neuropathy have also been described.
Episodic unconsciousness and paroxysmal limb weakness unrelated to posture, abnormal behavior, cognitive decline, and leptomeningeal enhancement reflect CNS involvement in patients 1 and 2. These, together with the presence of high CSF protein led to the mistaken diagnosis of TBM. TB is endemic to India and patients often receive “empirical” treatment. Another patient from India with genetically established FAP and treated for abdominal TB has been reported. Biopsy of brain and leptomeninges was not performed in our patients. Nevertheless, the characteristic MRI appearance, concomitant clinical features, presence of amyloid in peripheral tissues, and pathogenic mutations in TTR suggests that intracranial pathology is likely to be due to leptomeningeal amyloidosis.
Leptomeningeal amyloidosis is rare and clinical features include headache, seizures, vertigo, dementia, psychosis, ataxia, spasticity, impaired vision/hearing, reduced respiratory drive, myelopathy, hemorrhage, and hydrocephalus., There is an extensive thickening of leptomeninges and subarachnoid vessels. Hemorrhages often occur from the fragile amyloid laden vessels. CSF protein is elevated and may appear xanthochromic. It is often accompanied by vitreous opacities that stain positive for amyloid, and hence, the term “oculoleptomeningeal” amyloidosis. This entity was first reported by Goren, and subsequently in patients of American, Japanese, Swedish, and African origin.,, In our cohort, patients 1 and 2 had evidence of leptomeningeal involvement, whereas none had vitreous opacities. Venkatesh et al. reported two pedigrees from India with ocular amyloidosis without leptomeningeal involvement.
The mechanism of episodic altered sensorium is intriguing in our patients since it was independent of orthostatic hypotension, and metabolic abnormalities and nonconvulsive status epilepticus were excluded. Previous studies showed amyloid deposition in the walls of medium- and small-sized arteries and arterioles, which reduces as the vessels penetrate the brain parenchyma. These pathological changes induce cerebral infarction/hemorrhage, subarachnoid hemorrhage, and/or hydrocephalus. Brain imaging in our patients did not show any of these changes other than leptomeningeal enhancement. Luminal narrowing due to amyloid deposition coupled with impaired autoregulation arising from dysautonomia causes cerebral ischemia without infarction and this may be the mechanism of paroxysmal weakness of limbs in our patients.
Other manifestations include cardiomyopathy, nephropathy, nodular cutaneous amyloidosis, pulmonary amyloidosis, and anemia. Cardiac manifestations include increased ventricular wall thickness, homogenous atrioventricular valve thickening, “sparkling” appearance of myocardium, and pericardial effusion. Increased ventricular wall thickness contrasts with low or normal QRS voltage, which was initially overlooked in patient 1. Repolarization abnormalities, conduction blocks, arrhythmias, congestive cardiac failure, and sudden cardiac death may occur.
Presence of amyloid on histological studies and pathogenic TTR mutations in genetic analysis helps to clinch the diagnosis. Histological studies can be carried out on nerve, salivary gland, abdominal fat, intestinal mucosa, endomyocardium, and on tenosynovial tissues obtained at carpal tunnel release surgery. Biopsy interpretation is observer dependent and tissue has to be meticulously scrutinized with serial and step sections since amyloid deposits may be patchy. Specific staining for amyloid viz. Congo red and examination under polarized microscope demonstrates apple-green birefringence and confirms the diagnosis. The sensitivity and specificity of 3-mm punch skin biopsy in detecting amyloid is 70% and 100%. Immunolabeling by TTR antibodies is the preferred technique to demonstrate amyloid. Scintigraphy using serum amyloid P is available in select centers and it permits semiquantitative evaluation of the extent and distribution of amyloid in various viscera.
Genetic studies confirm the diagnosis. The type of mutation may determine the phenotype, age at onset, and speed of progression. V30M, the commonest reported mutation, is associated with neuropathy. Val122Ile, Ile68Leu, Thr60Ala, and Leu111Met have cardiomyopathy as the dominant manifestations. Some mutations are associated with onset in upper limbs in the form of carpal tunnel syndrome. In the United Kingdom, T60A and V30M are the commonest mutations. T60A is associated with late-onset, severe sensorimotor polyneuropathy; carpal tunnel syndrome is frequent and multisystem involvement may occur early. In another center, Thr60Ala was the commonest mutation. Mutations causing leptomeningeal amyloidosis include A18G, A36P, A25T, G53A, G53G, L12P, P64S, Ser44, T114C, T49P, T69H, V30G, V30M, and Y114C., L12P mutations have been associated only with oculoleptomeningeal amyloidosis in European descent and in an occasional subject of African origin. Y69H variant causes leptomeningeal amyloidosis, which is characterized by episodic exacerbations, ocular involvement, and rarely polyneuropathy. We report a family of Indian origin with p. Gly73Ala mutation associated with phenotype of leptomeningeal amyloidosis, neuropathy, dysautonomia, cardiomyopathy, thyromegaly and onset in third decade, and autosomal dominant inheritance. This variant has been reported from Sweden and the United Kingdom in association with leptomeningeal and cardiac amyloidosis. While patient 1 had significant peripheral neuropathy leading to foot drop, patient 2 (brother) had no evidence of sensorimotor impairment on clinical examination. Patient 3 had a dominant neuropathy phenotype with cutaneous involvement and harbored p. Val91Ala mutation in TTR. Leptomeningeal enhancement was noted in the MRI. This variant has been reported from France and Spain in association with peripheral neuropathy, carpal tunnel syndrome, and ocular involvement. Mutant TTR from choroid plexus is the least stable variant.
Treatment is aimed at suppressing the production of mutant amyloid as well as symptomatic treatment of specific organ dysfunction. Liver transplant, the first-line therapy, removes the source of mutant TTR, prevents progression of polyneuropathy, and improves survival. But worsening of function of other organs like heart, kidney, and eyes may continue. Outcome following liver transplantation in leptomeningeal amyloidosis is variable. De novo leptomeningeal amyloid deposition may occur following liver transplantation as it removes the variant TTR from blood only. Drugs that stabilize TTR viz. tafamidis and diflunisal slow the progression of neuropathy and are recommended in early stages. Antisense oligonucleotides, small interfering RNA, and antiserum amyloid P monoclonal antibodies block hepatic production of mutant TTR. However, none of the therapies is effective in leptomeningeal amyloidosis. Doxycycline brought about improvement in cognitive functions and gait in a patient with Y69H mutation and leptomeningeal amyloidosis. Thus, different therapeutic strategies such as stabilizers of TTR tetramers and gene therapies to suppress TTR expression are being used with effective results. A number of “nutraceticals” are being evaluated for their potential role in treatment of FAP. Our patients were not suitable candidates for liver transplant because of long duration and advanced stage of disease and significant leptomeningeal involvement. This emphasizes the need for early diagnosis.
TTR mutations cause the most common type of autosomal-dominant hereditary systemic amyloidosis viz. FAP. Diagnosis is sometimes delayed, especially in patients without a clear family history and typical clinical manifestations. Clinical diagnosis of FAP may be considered in any patient presenting with multisystem involvement affecting central and peripheral nervous system and dysautonomia in the presence of family history. Hypertrophic cardiomyopathy in the absence of hypertension or evidence of left ventricular hypertrophy in electrocardiogram and thyromegaly without deranged thyroid functions should further heighten the diagnostic suspicion. It is important to remember that a negative biopsy does not exclude. Demonstrating amyloid deposits is sometimes difficult, especially in cases of late-onset; hence, it is not absolutely mandatory to demonstrate this deposit, and in order to avoid delay in diagnosis, priority should be given to early genetic testing. The importance of establishing accurate diagnosis lies in the fact that these patients may be candidates for upcoming therapies.
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[Figure 1], [Figure 2], [Figure 3]