[Stiff person syndrome is a rare autoimmune disorder].

Atypical symptoms raise classical diagnostic dilemmas of somatic versus functional disease. The challenge is greater when the condition is less frequent. Illustrating this issue is a case of stiff person syndrome (SPS) where a 46-year-old man was admitted with lower back and hip pain and stiffness of the musculature of the lower extremities resulting in stooped gait. Stiffness was absent while sleeping. Thorough clinical examination and tests were unable to explain the symptomology until suspicion of SPS was raised, supported by high levels of glutamic acid decarboxylase antibodies.