General description

Paraneoplastic neuropathy (PNN) is a neurological disorder associated with cancer, caused not by direct tumor invasion, treatment toxicity, metabolic disturbances, or infections, but by an immune-mediated "bystander" effect on the nerves. PNN primarily affects the dorsal root ganglia, leading to severe sensory ataxia that typically develops subacutely and is often progressive, though occasionally follows a slower course.

The condition is most commonly seen in individuals in their 50s and 60s and often presents with sensory symptoms such as numbness and paresthesia, usually beginning in both hands and showing asymmetry. Patients experience reduced pain and temperature sensation, along with impaired vibration and position sense, resulting in sensory ataxia. Mild muscle weakness may also occur. Cranial nerves, including the oculomotor, trigeminal, facial, and vestibulocochlear nerves, are frequently involved, with subacute sensorineural hearing loss being the most common cranial nerve symptom in anti-Hu antibody-associated PNN.

PNN is often associated with small cell lung cancer and, less commonly, with gastric or breast cancer. It may coexist with other paraneoplastic syndromes, such as limbic encephalitis, meningoencephalitis, brainstem encephalitis, or cerebellitis.

Radiographic features

MRI shows T2WI hyperintensity in the posterior column of the spinal cord, reflecting secondary degeneration of the posterior root or dorsal root ganglion. Additionally, MRI reveals contrast enhancement in cranial nerves, including the oculomotor, trigeminal, facial, and vestibulocochlear nerves.