Step1 Question of the Week #5
A 23-year-old woman comes to her physician’s office for a follow up visit. She had recently been involved in a traumatic road traffic accident, where she fractured a few bones and also suffered from a mild concussion. There was no apparent injury to the brain evident on any diagnostic tests. She was kept under observation in the ICU for 24 hours and was then sent home with her family. It has been one month since the accident. Today, she has not complaints and says that she has been recovering well since the incident. Her only concern is that she has been losing weight unintentionally over the past month. She says that she doesn’t have much of an appetite and has to force herself to eat her daily meals. She has lost almost 7kgs since her accident. Her physician suspects a possible lesion to the brain that was probably not evident during the initial investigation. Based on her medical history, which of the following locations likely sustained an injury during her accident?
(A) Dorsomedial thalamic nuclei
(B) Lateral hypothalamic nuclei
(C) Ventromedial hypothalamic nuclei
(D) Ventral posterolateral thalamic nuclei
(E) Hypothalamic mammillary body
1 Comment
Correct Option B: Based on the history and symptoms described in the present case, the patient likely has a lesion in her hypothalamus. A lesion to the lateral nucleus leads to a decreased appetite and weight loss.
The hypothalamus, a part of the diencephalon, is present beneath the thalamus and has several nuclei. These nuclei receives afferent and efferent connections to and from various parts of the nervous system and endocrine system. Its primary function is to maintain homeostasis through various mechanisms. Any damage to the hypothalamus can cause significant and apparent dysfunction in normal homeostatic functions.
The several nuclei present in the hypothalamus control several different functions relating to hunger, temperature and certain personality aspects. Birth defects, tumours, trauma, infections and other metabolic disturbances can all affect the functioning of the hypothalamus. In several instances, the cause of hypothalamic dysfunction cannot be related to a certain event and is thus classified as idiopathic hypothalamic dysfunction. Based on the clinical presentation, the location of the nuclei affected can be determined.
The lateral hypothalamic zone is the feeding center of the hypothalamus. A lesion or injury to this part of the hypothalamus can lead to a loss in appetite and eventually weight loss. The extent of aphagia depends on the extent of the damage to the hypothalamic nuclei.
Incorrect Option A: Lesions to the dorsomedial thalamic nuclei leads to Wernicke’s encephalopathy. Malnutrition and excessive alcoholism causes thiamine deficiency which in turn causes this encephalopathy. Ataxia and ophthalmoplegia can also occur as a result. Thiamine supplementation is one of the primary ways to treat Wernicke’s encephalopathy.
Incorrect Option C: The ventromedial nuclei in the hypothalamus is responsible for regulating food intake. Lesions to this nucleus in the hypothalamus can result in weight gain and eventual obesity.
Incorrect Option D: Lesions to the ventral posterolateral nuclei in the thalamus result in central thalamic pain. Stroke, trauma or injury can cause symptoms of Dejerine-Roussy syndrome. Patients experience hemianesthesia, loss of vibration and proprioception to the contralateral side of the body. Patients also exhibit dysesthesia, which is a heightened sense of pain to the slightest stimuli.
Incorrect Option E: The mammillary bodies are present in the posterior region of the hypothalamus. They contain the mammillary nuclei that connect to the anterior nuclei of the thalamus. Progressive thiamine deficiency can cause lesions to the mammillary bodies. This causes Korsakoff syndrome where there is antegrade and retrograde amnesia.
Learning Objective:
The region just below the thalamus is known as the hypothalamus. It has several nuclei that control a diverse array of functions. It is a part of the diencephalon along with the thalamus and epithalamus. Congenital anomalies, genetic disorders, trauma, infections and metabolic dysfunctions can all disrupt hypothalamic function. In some cases, the cause is unknown. The lateral and ventromedial nuclei of the hypothalamus control appetite. Lesion to the lateral nuclei cause aphagia and lesion the the ventromedial causes weight gain through an increase in appetite.