Familial Amyloid Polyneuropathy (FAP): an important differential diagnosis of leprosy neuropathy

A 64-year-old male with a family history of leprosy and cardiomyopathy presented with paresthesia and neuropathic pain in the lower limbs for one year, progressing to the upper limbs for the last 6 months, besides erectile dysfunction for at least 3 years and episodes of postural hypotension. Due to the family history, primary neural leprosy (PNL) was suspected. The nerve conduction study showed a severe, predominantly sensory, axonal, symmetrical, chronic axonal polyneuropathy with signs of acute denervation, and laboratory tests for PNL were negative. A peripheral nerve biopsy (sural) showed amyloid deposits and molecular evaluation confirmed the diagnosis of Familial Amyloid Polyneuropathy (FAP). Specific treatment for FAP was started and the family members were evaluated, confirming that many had FAP and were misdiagnosed as leprosy. This case shows the importance of differentiating PNL and FAP in clinical practice. We propose a table to help distinguish these two conditions in clinical practice.