Diagnostic pitfalls in sporadic transthyretin familial amyloid polyneuropathy (TTR-FAP)

We read the article by Planté-Bordeneuve et al. with great interest. [1] We reported a unique patient with sporadic TTR (Val30Met) -FAP [2] and have inquiries regarding the sporadic patients of Planté-Bordeneuve et al. [1]

Our patient, a 72-year-old man, developed dysesthesisa and weakness in the feet at age sixty-seven. Two years later, severe muscle weakness and loss of sensation progressed rapidly in the four extremities. His family history showed no neurological or cardiac disorders.

Neurological examination showed muscle weakness (MRC 0-1) and profound atrophy in the hands and feet. Muscle stretch reflexes were absent in the four extremities. Dysarthria and dysphagia were found and marked atrophy and fasciculation were seen in the tongue. Pharyngeal reflexes were absent. There were no superficial and proprioceptive sensations in the hands and feet. There was no dysautonomia including postural hypotension, gastrointestinal or sphincter dysfunction.

Cerebrospinal fluid tests showed mild increase of protein (58 mg/dL). Sensory nerve conduction velocities were not evoked in the four extremities. Motor nerve conduction velocities were not evoked in the tibial and peroneal nerves. Needle electromyography revealed positive sharp waves and fibrillation potentials in the distal limb and tongue muscles.

Sural nerve biopsy showed severe loss of myelinated fibers without amyloid deposits. The patient died of renal failure. Immunohistochemical study disclosed TTR-amyloid deposits in the median nerve and the hypoglossal nerve root. Gene analysis of FAP indicated Val30Met mutation. Planté-Bordeneuve et al. review mild dysautonomia and prominent large myelinated fiber sensory loss in late-onset patients with Val30Met FAP-TTR. [1] Those clinical hallmarks are similar to our patient. We would like to know the clinico-pathological findings in patients with senile onset (more than 65 years) among their 90 patients with sporadic FAP. What are the different features between patients with early versus senile onset?

It is interesting that six patients had uncommon cranial nerve involvement. The second question is whether those patients have typical histories of FAP-TTR. Specifically, we would like to see bulbar and limb motor deficits in one patient with the Val30Met mutation and bilateral hypoglossal nerve palsy.

Misdiagnosis of nonfamilial TTR-FAP in senile-onset patients who have rapid progression of sensorimotor neuropathy and normal autonomic function is possible. TTR gene analysis in these patients should be considered to avoid diagnostic delay.

References

1. Planté-Bordeneuve V, Ferreira A, Lalu, T, et al. Diagnostic pitfalls in sporadic transthyretin familial amyloid polyneuropathy (TTR-FAP). Neurology 2007;69:693-698.

2. Ikeda K, Kinoshita M, Takamiya K, et al. Bulbar palsy in senile onset familial amyloid polyneuropathy (30Val�¨Met): transthyretin-amyloid deposits in the hypoglossal nerve root. Eur J Neurol 1998;5:211-214.

Disclosure: The authors report no conflicts of interest.

We would like to thank Dr. Ikeda et al. for their interest in our article on sporadic familial amyloid polyneuropathy (FAP). [1] It is difficult to accurately compare the nerve pathology of patients with early and late onset FAP because the interval between performance of the biopsy and the onset of clinical manifestations varies.

However, we also observed that large myelinated fibers are more affected in late onset cases, with less involvement of unmyelinated fibers than in early onset FAP. [3] Cranial nerves are more often affected in late onset FAP with occasionally pure motor neuropathies mimicking motor neuron disease, as we also observed recently (unpublished data).

Therefore, if FAP generally presents as a length dependent sensory-motor polyneuropathy with life threatening autonomic dysfunction, many exceptions occur which may delay diagnosis and treatment. In younger patients, the classic pattern is the most common, while in the elderly presentation it is variable and often misleading with asymmetrical onset, ataxia, or predominantly motor deficit with little or no autonomic dysfunction.

In addition, the clinician must consider the many diagnostic pitfalls in late onset FAP, which is why we shared our experiences.

Reference

3. Said G. Familial amyloid polyneuropathy: mechanisms leading to nerve degeneration. Amyloid 2003; 10, Suppl.1, 7.

Disclosure: The authors report no conflicts of interest.