By Carolyn A. Scott, Ph.D., CBIST
Rainbow Rehabilitation Centers

When individuals think about the effects of a traumatic brain injury (TBI) on the body, they may think about muscle weakness or spasticity, difficulty communicating, slowed thinking, etc. The effects of the injury on our endocrine system may be less obvious to outside observers. However, endocrine dysfunction as a result of TBI can significantly influence daily functioning, and yet it is frequently overlooked.

What is the endocrine system?

The endocrine system is a group of ductless glands that regulate body processes through the secretion of chemical substances called hormones1. The endocrine system is distributed throughout the body. It includes the hypothalamus, pituitary gland, pineal gland, thyroid, parathyroid gland, pancreas, adrenal glands, testes, and ovaries. For the purpose of this article, the focus will be on those structures within the brain, the hypothalamus, pituitary gland, and pineal gland.

TBI and endocrine dysfunction

Traumatic brain injury is known to affect the brain through primary and secondary means. Primary injury includes localized injury, such as a bleed, and diffuse axonal injury as a result of axonal stretching, tearing, and shearing. Secondary mechanisms of injury include swelling, low oxygen, increased cranial pressure, and neurochemical cascade. Damage to the hypothalamus and pituitary gland is known to occur after TBI. These structural changes may include lesions of the hypothalamic-pituitary stalk, anterior lobe necrosis, and posterior lobe hemorrhage.2 In the anterior lobe of the pituitary gland, lesion is typically caused by infarction.3 Swelling can also cause damage due to the relatively confined space within which the pituitary gland is located.3 Lesion in the posterior lobe is most commonly due to acute hemorrhage.3

These types of injuries are not uncommon. One study found that during autopsy, up to a third of fatal TBIs involved pituitary gland necrosis.4 Other research has demonstrated that lesions to the hypothalamus were common after TBI, occurring in 42% of fatal brain injuries.5

Neuroendocrine conditions that are commonly seen after TBI include syndrome of inappropriate antidiuretic hormone (SIADH), diabetes insipidus, and anterior hypopituitarism. Diabetes insipidus is due to failure of antidiuretic hormone (ADH) to release as a result of damage to the posterior pituitary lobe. The most common symptoms are excessive thirst and diluted urination. SIADH causes dilution of blood and low sodium secondary to too much ADH. Symptoms include fatigue, weakness, muscle cramps, decreased appetite, increased thirst, nausea/vomiting, seizures, confusion and change in urinary habits. Symptoms of hypopituitarism is specific to which hormone is deficient. Individuals with this condition may be asymptomatic initially.

DefinitionsOccurrence of neuroendocrine dysfunction after TBI

Rates of pituitary dysfunction among survivors of TBI have been estimated between 37-59%.6,7 Other estimates of hormonal abnormalities have been even higher.8 In some research, rates of dysfunction have been suggested to be dependent on the severity of injury with greater dysfunction in the more seriously injured.6 Other research does not show a clear relationship between severity of injury (as measured by Glasgow Coma Scale) and the presence of pituitary dysfunction.8 Varying rates of hormone deficiencies were found immediately after injury and 12 months after injury with growth hormone deficiency being the most commonly found deficiency (37.7% of the sample one year post TBI).7

Neuroendocrine dysfunction and daily functioning

Neuroendocrine dysfunction may aggravate the physical and neuropsychiatric morbidity after TBI.9 Symptoms of neuroendocrine dysfunction are similar to the symptoms seen after TBI. These include: depression, emotional lability, anxiety, fatigue, poor memory, difficulty concentrating, low libido, infertility, amenorrhea, loss of muscle mass, weight gain or loss, increased adipose tissue around the belly, low blood pressure, reduced heart rate, anemia, constipation, cold intolerance, and dry skin.10 The overlap in presentation likely contributes to the tendency to overlook endocrine dysfunction and focus solely on TBI.

Fortunately, there are methods to assess endocrine dysfunction. Neuroimaging can help visualize damage to the hypothalamus or pituitary gland. Blood tests can be used to evaluate hormone levels. Assessing hormone levels acutely and then in the post-acute phase has been recommended. Specifically, evaluation of pituitary function and growth hormone reserve was recommended for all survivors of moderate to severe TBI one year post injury.11 Working with an endocrinologist familiar with TBI may be helpful to facilitate the recognition of deficiencies and ensure proper treatment. As part of a TBI treatment team, an endocrinologist may prescribe medications and hormone replacement therapy to address endocrine dysfunction as a result of TBI.

In summary, endocrine dysfunction is common after traumatic brain injury. Since many of the signs of hormone deficiency are similar to the cognitive, behavioral, and somatic symptoms experienced after TBI, endocrine dysfunction may be easily overlooked. Given that many of these deficiencies can be addressed medically, it is important to work with a physician for assessment and treatment of endocrine dysfunction when appropriate. If you have questions or concerns about your own endocrine function, contact your medical provider.  ❚

Endocrine-diagram

How the endocrine system works

The hypothalamus is in the ventral diencephalon area of the brain. Put more simply, it is located towards the base and middle of the brain. The hypothalamus is made up of several nuclei or small zones with distinct functional roles. However, as a unit, it serves to regulate homeostasis, controls the autonomic nervous system and visceral functions, and regulates appetite, temperature, thirst, stress response, lactation and cardiorespiratory function. It also has a role in the limbic system, an area of the brain that influences our emotions and behaviors.

In addition to serving as a connection between the endocrine and nervous system, the hypothalamus has projections to multiple areas of the brain. These projections demonstrate the multiple ways that the brain works as a cohesive unit. For example, the hypothalamus receives information from the retina, cerebral cortex, amygdala, and hippocampus. Some of the areas to which the hypothalamus sends information include the thalamus, brainstem, and pituitary gland.

The pituitary gland is approximately the size of a pea and is connected to the base of the hypothalamus via a stalk. It can be divided into two portions; the anterior lobe (at the front or towards the face) and the posterior lobe (towards the back of the head). The lobes have different roles and secrete different hormones. The anterior lobe regulates the thyroid, adrenal glands, and gonads. It also produces growth hormone, prolactin, thyrotropin, and corticotropin. The function of the anterior lobe is regulated by the hypothalamus. The posterior lobe of the pituitary gland, which is an extension of the hypothalamus, secretes two hormones produced in the hypothalamus; vasopressin (also called antidiuretic hormone or ADH) and oxytocin (see sidebar page 10 for definition of terms).

The pituitary gland also secretes endorphins, chemicals that act on the nervous system and reduce feelings of pain.12 In addition, the hormones produced by the pituitary gland influence the production of sex hormones via the testes and ovaries.13 The pituitary gland also controls ovulation and the menstrual cycle in women.

Also located in the brain, the pineal gland or pineal body produces melatonin which regulates our circadian rhythms. Circadian rhythms are the internal clock that regulates biological and behavioral processes.

The hormones that are produced and secreted throughout the endocrine system travel through the bloodstream to act on specific targets. Oversecretion or undersecretion of hormones or the inability of the targets to effectively use the hormones causes endocrine dysfunction.1

About the Author

Carolyn A. Scott, Ph.D., CBIST
Psychologist

Dr. Scott earned her Ph.D. in Clinical Psychology at Wayne State University. After an internship at the John D. Dingell VA Medical Center, she completed specialized post-doctoral training in Neuropsychology and Rehabilitation Psychology at the Rehabilitation Institute of Michigan. While there, Dr. Scott worked with individuals who had experienced traumatic brain injuries, stroke, spinal cord injuries, and other neurological and orthopedic conditions on both an inpatient and outpatient basis. In addition to other responsibilities, Dr. Scott provides client and team consultation services and brief and expanded neuropsychological evaluations at Rainbow Rehabilitation Centers, Inc.

References

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