Carpal tunnel syndrome is one of the most common conditions encountered in general neurological practice, the usual cause being occupational activities using repeated wrist movement such as housework, typing or gardening. Under normal conditions, the carpal tunnel is already crowded with structures including nerves and tendons, with little extra space to accommodate expansion of its contents. Any increase in volume may have a significant impact on its clinically most sensitive structure, the median nerve.1 In most cases, symptoms arise simply from excessive use of the hand producing friction and swelling of the nerve. Additional pathological conditions affecting the carpal tunnel include diabetes mellitus, pregnancy, tumours, myeloma, myxoedema, acromegaly and pathological enlargement of joints or tendons such as in rheumatoid arthritis.2 3 However, we have recently encountered an unusual cause for this otherwise common clinical condition, which clinicians should be aware of during normal clinical practice.