Apathy is a clinical syndrome characterized by a reduction in motivation, self-initiated and goal-directed behaviors, and emotional indifference (Levy and Dubois, 2006; Stuss et al., 2000). Historically, the construct of apathy was thought to be collinear with depression (Teixeira et al., 2021); indeed, both syndromes can involve anhedonia, diminished interest in pleasurable activities, and blunted affect (Brodaty and Connors, 2020). However, the clinical presentation of apathy can differ from depression along multiple dimensions (e.g., rumination, suicidality, and anxiety are not typically present in apathy; Mortby et al., 2022). Furthermore, it has become clear that depression is neither necessary nor sufficient for a diagnosis of apathy, which can be present in the absence of depression and vice-versa (Kirsch-Darrow et al., 2011; Starkstein et al., 2001). To this end, mounting evidence from numerous behavioral, psychological, and neuroimaging studies suggest that apathy can be characterized as its own unique neuropsychiatric syndrome that is separate from depression (Chen et al., 2021; Husain and Roiser, 2018; Teixeira et al., 2021).

It is estimated that clinically significant apathy occurs in approximately 2 % and 6 % of healthy younger and older adults, respectively (Brodaty et al., 2010; Pardini et al., 2016). Emerging studies are exploring facets of subclinical apathy (e.g., emotional, behavioral/initiative, and cognitive/executive apathy) that may occur in roughly one-third of healthy adults (Ang et al., 2017; Lafond-Brina and Bonnefond, 2022). The presence of apathy interferes with the completion of many daily activities, including preparing meals, household chores, managing finances and medications, and planning outings (Lam et al., 2007). Apathy is also associated with more rapid progression of neurodegenerative diseases (Salem et al., 2023) and caregiver burden (Nobis and Husain, 2018). Specific neural substrates of apathy revolve around the prefronto-striatal pathway that includes the anterior cingulate cortex, orbitofrontal cortex, nucleus accumbens, and thalamus (Chen et al., 2021; Gonçalves et al., 2020).

As such, apathy is an important clinical consideration for conditions that affect the integrity of these prefronto-striatal pathways, including some patients with neurodegenerative disease (Abdollah Zadegan et al., 2023; Nobis and Husain, 2018), stroke (Tay et al., 2021), psychiatric disorders (Stuss et al., 2000), and some infectious diseases (Walker and Brown, 2018). Apathy is commonly observed in persons infected with the human immunodeficiency virus (HIV). Viral proteins can infiltrate the central nervous system (CNS) early in the course of HIV infection, where they preferentially target the prefronto-striatal pathways (Ellis et al., 2007). HIV can exert both direct (e.g., viral protein toxicity) and indirect (e.g., inflammatory, immune, vascular) effects on the structure and functions of the prefrontal-striatal pathways (Kamkwalala and Newhouse, 2017). As a consequence of diverse neuropathophysiological processes affecting the prefrontal-striatal connections, persons living with HIV (PLWH) can develop a constellation of cognitive, motor, and neuropsychiatric complications, including apathy (Kieburtz et al., 1991; McLaurin et al., 2021).

Seminal papers from the 1980s that first characterized AIDS Dementia Complex (ADC) and HIV-Associated Dementia (HAD) recognized apathy as a prominent clinical feature. The earliest study to mention apathy in HIV disease was published by Navia and colleagues in 1986, who noted that apathy and social withdrawal were some of the earliest behavioral changes observed in HAD. Qualitatively, patients who were previously outgoing demonstrated emotional indifference, reduced interest in social or vocational activities, and limited verbal initiation (Navia et al., 1986). Diederich et al. (1988) later commented that clinical signs of lethargy and reduced motivation in HAD provided evidence that HIV infection had impacted the CNS. A review characterizing the pathology and treatment of HAD in the era before combination antiretroviral therapies (cART) reported that apathy, social withdrawal, or depression were present in approximately 50 % of PLWH (Dal Canto, 1989). In recognition of the frequency and clinical importance of apathy in PLWH, the 1991 American Academy of Neurology AIDS Task Force included apathy in the criteria for a diagnosis of probable HIV-1-Associated Dementia Complex (Janssen et al., 1991).

Although the introduction of cART in the mid-1990s transformed HIV into a manageable chronic health condition for PLWH who can access and adhere to modern care regimens, the prevalence and functional impact of HIV disease on the structure and function of the CNS persists (Hammer et al., 1997; McLaurin et al., 2021). As such, there has been a rise in the number, rigor, and diversity of studies on apathy in PLWH during the cART era. The first study to use a formal measure of apathy in a sample of PLWH was conducted in the cART era (Castellon et al., 1998). The authors used the brief interview format of the Neuropsychiatric Inventory (Cummings et al., 1994) and found that higher apathy was significantly related to poorer working memory at a medium-to-large effect size. In 2018, a meta-analysis by Walker & Brown reported a large, pooled effect size for HIV on apathy symptom severity (d = −0.87) that was based on eight studies of PLWH (k = 311) and seronegative (k = 196) adults. There is a plethora of studies on the sociodemographic (e.g., age; Milanini et al., 2017), neurocognitive (e.g., McLaurin et al., 2021), psychiatric (e.g., Kamat et al., 2015), biological (e.g., Woods et al., 2022), and functional (e.g., Kamat et al., 2012, Kamat et al., 2013) correlates of apathy in HIV disease. However, to date no systematic integration and interpretation of the clinical prevalence and correlates of apathy in HIV disease has been conducted. Such an undertaking is important given the potentially serious implications of apathy for difficulty managing HIV as a chronic medical disease, which in turn contributes to further downstream medical, neurocognitive, psychological, and functional consequences for PLWH (Cysique and Brew, 2019a). The breadth and diversity in these goals lend itself to a systematic narrative review to examine and summarize the presence and clinical correlates of apathy among PLWH in the extant literature.