Musical hallucinations fall under the category of auditory hallucinations and describe a disorder in which a sound is perceived as instrumental music, sounds, or songs. It is a very rare disorder, reporting only 0.16% in a cohort study of 3,678 individuals.
In 73 individual cases reviewed by Evers and Ellger, 57 patients heard tunes that were familiar, while 5 heard unfamiliar tunes. These tunes ranged from religious pieces to childhood favorites, and also included popular songs from the radio. Vocal and instrumental forms of classical music were also identified in most patients. Keshavan found that the consistent feature of musical hallucinations was that it represented a personal memory trace. Memory traces refer to anything that may seem familiar to the patient, which indicate why certain childhood or familiar songs were heard.
Musical hallucinations can occur in people who are physically and mentally healthy, and for them, there is no known cause.  Most people find their musical hallucinations obtrusive, and wish to be rid of them, while others welcome them. In addition, investigators have pointed to factors that are associated with musical hallucinations. Evers and Ellgers compiled a significant portion of musical hallucination articles, case studies etc. and were able to categorize five major etiologies:
Hypoacusis is defined as impairment in hearing or deafness. Hypoacusis is one of five etiologies of musical hallucinations, and is the most common in the case studies reviewed by Evers and Ellgers. According to Sanchez et al. 2011, there have been suggestions that pontine lesions could alter the central auditory system's function causing hypoacusis and musical hallucinations.
A case study by Janakiraman et al. 2006, revealed a 93‑year‑old woman with major depressive disorder who experienced musical hallucinations while treated with electroconvulsive therapy (ECT). Investigators found that the patient's depression symptoms were inversely related to her hallucinations and primarily stemmed from the ECT treatment. The patient had no known abnormalities in hearing, suggesting that musical hallucinations could arise from a variety of sources including psychiatric illnesses. After a complete course of ECT, her hallucinations dissipated, also suggesting that they can be acute.
According to Evers and Ellgers, some other major psychiatric disorders that contribute to musical hallucinations include schizophrenia and depression. Some patients who have schizophrenia experience musical hallucinations due to their ongoing psychosis, but there are some cases that do so without psychosis. There are also a very small percentage of musical hallucination cases due to obsessive-compulsive disorder (OCD).
Focal brain lesions
Among the handful of cases that Evers and Ellgers studied, major lesion sites included the temporal cortex; however, the specific location and laterality (left vs. right temporal cortex) was variable. Many cases of focal brain lesions had comorbidity with hearing impairment (see hypoacusis), epileptic activity and intoxication. There have also been several findings of acute musical hallucinations in patients with dorsal pons lesions post-stroke and encephalitis potentially due to disruption of connections between the sensory cortex and reticular formation.
Epileptic brain activity in musical hallucinations originates in the left or right temporal lobe. In a specific case studied by Williams et al. 2008, a patient who received a left temporal lobectomy in order to treat epilepsy was diagnosed with musical hallucinations post-surgery. The patient also had multiple additional risk factors that could have accounted for the hallucinations including mild neuropsychiatric dysfunction and tinnitus.
Intoxication accounts for a small percentage of musical hallucination cases. Intoxication leads to either withdrawal or inflammatory encephalopathy, which are major contributors to musical hallucinations. Some of the drugs that have been found to relate to musical hallucinations include salicylates, benzodiazepines, pentoxifylline, propranolol, clomipramine, amphetamine, quinine, imipramine, a phenothiazine, carbamazepine, marijuana, paracetamol, phenytoin, procaine, and alcohol. General anesthesia has also been associated with musical hallucinations. In a case study by Gondim et al. 2010, a seventy–seven-year-old woman with Parkinson's disease (PD) was administered amantadine after a year of various other antiparkinsonian treatments. Two days into her treatment, she started to experience musical hallucinations, which consisted of four musical pieces. The music persisted until three days after cessation of the drug. Although the patient was taking other medications at the same time, the timing of onset and offset suggested that amantadine either had a synergistic effect with the other drugs or simply caused the hallucinations. Although the case wasn't specific to intoxication, it leads to the idea that persons with PD who are treated with certain drugs can experience musical hallucinations.
Positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) show that musical hallucinations activate a wide variety of areas in the brain including the following: auditory areas, motor cortex, visual areas, basal ganglia, brainstem, pons, tegmentum, cerebellum, hippocampi, amygdala, and peripheral auditory system.
To date, there is no successful method of treatment that "cures" musical hallucinations. There have been successful therapies in single cases that have ameliorated the hallucinations. Some of these successes include drugs such as neuroleptics, antidepressants, and certain anticonvulsive drugs. A musical hallucination was alleviated, for example, by antidepressant medications given to patients with depression. Sanchez reported that some authors have suggested that the use of hearing aids may improve musical hallucination symptoms. They believed that the external environment influences the auditory hallucinations, showing worsening of symptoms in quieter environments than in noisier ones. Oliver Sacks' patient, Mrs. O'C, reported being in an "ocean of sound" despite being in a quiet room due to a small thrombosis or infarction in her right temporal lobe. After treatment, Mrs. O'C was relinquished of her musical experience but said that, "I do miss the old songs. Now, with lots of them, I can't even recall them. It was like being given back a forgotten bit of my childhood again." Sacks also reported another elderly woman, Mrs. O'M, who had a mild case of deafness and reported hearing musical pieces. When she was treated with anticonvulsive medications, her musical hallucinations ceased but when asked if she missed them, she said "Not on your life."
According to Oliver Sacks' Hallucinations, the first known medical report of musical hallucinations was published in 1846, by French alienist Jules Baillarger. However, the first scientific description of the disorder was reported in the early 1900s. In the last two decades, Berrios has reported case studies in 1990 and 1991 along with Keshavan et al. in 1992. Berrios concluded that confirmed diagnoses of deafness, ear disease, brain disease, advanced age and drug use are all important factors in the development of musical hallucinations. After analyzing 46 cases, Berrios found a female predominance of 80% in women over the age of 60. The study concluded that musical hallucinations were more likely to be seen in elderly women affected by deafness or brain disease than in individuals with no psychiatric illness at all.
Keshevan and Berrios were the first authors to identify classes of musical hallucinations. These classes consisted of hearing loss, coarse brain disease (i.e. tumors), epileptic disorder, stroke, and psychiatric disorder. Although no statistical analyses were performed, the authors stated that deafness was the most strongly related factor in musical hallucinations and that there was a female predominance, which could entail a genetic component.
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