Transthyretin amyloidosis is a rare disorder caused by the accumulation of misfolded transthyretin amyloid in organs. The symptoms can include neuropathy, cardiomyopathy, nephropathy, depression and cognitive decline. Because of the non-specificity of symptoms, it usually takes considerable time to diagnose, which delays specific therapy and leads to a worse prognosis. Our case highlights the psychological symptoms of this disorder that initially delayed diagnosis, and later helped to reach the correct diagnosis. We report the case of a man who presented with weakness of limbs, dizziness, vomiting, social withdrawal, loss of interest, reduced energy and difficulty concentrating. Different specialist evaluations failed to identify a cause, and the symptoms were attributed to depressive disorder. After psychiatric hospitalization to rule out depression as a possible cause, the patient was transferred to an internal medicine clinic where additional diagnostics led to a transthyretin amyloidosis diagnosis. Early-stage transthyretin amyloidosis is difficult to diagnose owing to its non-specific symptoms, but timely treatment is necessary to improve the disease course and outcome. With reference to this case, we emphasize that psychological symptoms in somatic illnesses can both delay and facilitate diagnosis of underlying disease.