Patients in France with FAP, Upper Limb Nerve Damage Often Misdiagnosed, Study Suggests

Familial amyloid polyneuropathy (FAP) with arm (upper limb) involvement is common in France and frequently missed because of incorrect diagnosis, a French study reported.

This study, “Upper Limb Onset of Hereditary Transthyretin Amyloidosis is common in Non‐Endemic Areas” was published in the European Journal Of Neurology.

FAP, or hereditary ATTR amyloidosis, is a genetic condition caused by a mutation in the transthyretin (TTR) gene. Abnormal deposits of proteins, or amyloids, around the nerves and tissues result in inflammation of the nerves (neuropathy) and associated symptoms that worsen over time.

It has been frequently reported in areas such as Portugal, but the condition has also been observed in non-endemic regions. In such places, cases usually present with uncommon characteristics, such as upper limb (arm) onset.

The researchers discussed FAP cases with hand manifestation from France, where FAP has not been frequently reported, and compared them to cases from Portugal.

The database for the French national reference center for FAP was used to identify study participants. A total of 32 TTR FAP patients with confirmed amyloid deposits were included.

These patients had a clinical onset of neuropathy in the upper limb (upper limb onset, or ULO), and symptoms of neuropathy in the legs that occurred after at least six months of hand neuropathy (ULO group). Their mean age at disease onset was 63.5 years.

The researchers found that 24 patients (75%) were initially misdiagnosed with 15 different conditions. Of the nine patients who were misdiagnosed with carpal tunnel syndrome (CPT), none  had any underlying cause for the diagnosis.

The most common symptoms reported by the ULO group were a tingling/pricking sensation (paraesthesia) and/or loss of sensation (anesthesia) in 81.2% of the patients and pain in 18.7% of the patients.

Within six months to 16 years after hand (upper limb) symptoms were reported, 96.8% (31) patients developed symptoms in the leg (lower limb).

Researchers found that 23 (71.8%) had undergone a nerve biopsy at some point. Of those, 11 were radial nerve (upper limb) biopsies, all of which revealed amyloid deposits in the tissues around the protective myelin sheath. A complete blockage was reported in two of the biopsies.

FAP is relatively common in Portugal (endemic area) compared with France, where it is rarely known (non-endemic), the authors stated. Researchers compared the data from the ULO group with that of 31 Portuguese patients with mean TTR onset age of 34.3 years  (early onset, or EO, group) and 91 patients with mean TTR onset age of 64.4 years without upper limb neuropathy (late onset, or LO group) to understand the differences between these populations.

A significantly higher number of patients in the LO group (15%) met the clinical criteria for chronic inflammatory demyelinating polyneuropathy (inflammation of nerve roots and destruction of the protective myelin layer) compared to 6.2% in the ULO group and none in the EO group.

Loss of reflexes and sensation in all four limbs was significantly more common in the ULO group compared to EO and LO groups.

Thus, “upper limb onset of hereditary ATTR neuropathy is not rare in non‐endemic areas,” the authors wrote. “It is important to propose early TTR sequencing of patients with idiopathic upper limb neuropathies, as specific management and treatment are required.”