# Internal Medicine/Numbness and Sensory Loss
## Introduction

Sensory abnormalities encompass a spectrum of experiences that can originate from various levels within the intricate neural network of the human nervous system. Understanding and interpreting these sensory anomalies is pivotal for effective diagnosis and treatment. This section serves as an introductory overview of the complex world of sensory aberrations.

## Types of Dysesthesias

Dysesthesias, characterized by abnormal and often unpleasant sensory sensations, pose a unique diagnostic challenge. They can manifest in a multitude of ways, making their interpretation a nuanced task. Here, we explore the diverse scenarios in which dysesthesias may arise, shedding light on their potential origins. These include systemic factors like hyperventilation or medication-induced occurrences, as well as signals of underlying neuropathies or myelopathies.

## Mapping Sensory Abnormalities

One of the crucial steps in deciphering sensory aberrations is the mapping of these anomalies. This section emphasizes the importance of this process in localizing the source of sensory disturbances. Focal nerve trunk lesions, for instance, often exhibit sensory abnormalities with well-defined boundaries. We delve into root ("radicular") lesions, where deep, aching pain frequently accompanies sensory deficits. Moreover, we discuss how isolated mononeuropathies may manifest symptoms beyond the territory supplied by the affected nerve, while polyneuropathies display graded, distal, and symmetric sensory deficits.

## Polyneuropathies

Polyneuropathies represent a vast category of sensory disturbances, each with its own unique characteristics. This section offers a detailed exploration of polyneuropathies, elucidating their distinct features. We differentiate between small-fiber and large-fiber polyneuropathies, highlighting their effects on various sensory modalities. Small-fiber polyneuropathies often manifest as burning, painful dysesthesias, while large-fiber polyneuropathies result in deficits in vibration and position sense, accompanied by imbalance and absent tendon reflexes.

## Sensory Neuronopathy

Sensory neuronopathy, or ganglionopathy, introduces a unique set of challenges in the realm of sensory disturbances. In this section, we delve into the characteristics of sensory neuronopathy. This condition is marked by widespread yet asymmetric sensory loss that can affect both the arms and legs. Our discussion revolves around the potential causes of sensory neuronopathy, including paraneoplastic origins, idiopathic cases, and associations with autoimmune diseases like Sjögren's syndrome.

## Spinal Cord

Spinal cord lesions can have profound effects on sensory perception. In this section, we explore the sensory implications of spinal cord lesions at different levels. We discuss the complete loss of sensation below the level of transection, lateral hemisections leading to the Brown-Séquard syndrome, and the occurrence of numbness or paresthesias in both feet—a potential indicator of a spinal cord lesion. Furthermore, we examine dissociated sensory loss and other sensations linked to spinal cord dysfunction.

## Brainstem

Brainstem lesions can result in unique patterns of sensory disturbances. This section delves into the sensory implications of lesions in the brainstem, including lateral medullary syndrome and pansensory loss. We explore how crossed patterns of sensory disturbance, affecting the face and the opposite side of the body, localize to the lateral medulla. Additionally, we consider the consequences of lesions in the brainstem tegmentum, where lemniscal and spinothalamic tracts converge.

## Thalamus and Cortex

Lesions in the thalamus and cortex can have a profound impact on sensory perception. In this section, we investigate the sensory disturbances that can arise from these brain regions. Hemisensory deficits, thalamic pain syndrome (Déjerine-Roussy syndrome), and cortical sensory seizures are among the phenomena explored. We examine the abrupt onset of sensory disturbances, often due to small strokes localized to the thalamus, and the unique experience of persistent, unilateral pain associated with thalamic lesions.

## Focal Sensory Seizures and Psychogenic Symptoms

Focal sensory seizures, often triggered by lesions in the postcentral or precentral gyrus, result in a range of sensory phenomena, including tingling and complex sensations. We explore the characteristics of focal sensory seizures, their unilateral nature, and their potential to progress to generalized seizures. Additionally, we consider the possibility of psychogenic symptoms causing sensory disturbances and discuss how they may manifest.

## Treatment

These can be the potential use of anticonvulsants and antidepressants to alleviate severe and persistent dysesthesias.