Review of Sickle Cell Disease and Spinal Pathology

A bone to pick-cellular and molecular mechanisms of bone pain in sickle cell disease

The bone is one of the most commonly affected organs in sickle cell disease (SCD). Repeated ischemia, oxidative stress and inflammation within the bone is largely responsible for promoting bone pain. As more individuals with SCD survive into adulthood, they are likely to experience a synergistic impact of both aging and SCD on their bone health. As bone health deteriorates, bone pain will likely exacerbate. Recent mechanistic and observational studies emphasize an intricate relationship between bone remodeling and the peripheral nervous system. Under pathological conditions, abnormal bone remodeling plays a key role in the propagation of bone pain. In this review, we first summarize mechanisms and burden of select bone complications in SCD. We then discuss processes that contribute to pathological bone pain that have been described in both SCD as well as non-sickle cell animal models. We emphasize the role of bone-nervous system interactions and pitfalls when designing new therapies especially for the sickle cell population. Lastly, we also discuss future basic and translational research in addressing questions about the complex role of stress erythropoiesis and inflammation in the development of SCD bone complications, which may lead to promising therapies and reduce morbidity in this vulnerable population.

Bone loss is ameliorated by fecal microbiota transplantation through SCFA/GPR41/ IGF1 pathway in sickle cell disease mice

Bone loss is common in sickle cell disease (SCD), but the molecular mechanisms is unclear. Serum insulin-like growth factor 1 (IGF1) was low in SCD subjects and SCD mice. To determine if decreased IGF1 associated with low bone mass in SCD is due to reduced SCFA production by gut microbiota, we performed reciprocal fecal microbiota transplantation (FMT) between healthy control (Ctrl) and SCD mice. uCT and histomorphometry analysis of femur showed decreased bone volume/total volume (BV/TV), trabecular number (Tb.N), osteoblast surface/bone surface (Ob.S/BS), mineralizing surface/ bone surface (MS/BS), inter-label thickness (Ir.L.Th) in SCD mice were significantly improved after receiving Ctrl feces. Bone formation genes Alp, Col1, Runx2, and Dmp1 from SCD mice were significantly decreased and were rescued after FMT from Ctrl feces. Transplantation of Ctrl feces increased the butyrate, valerate, and propionate levels in cecal content of SCD mice. Decreased G-coupled protein receptors 41 and 43 (GPR41 and GPR43) mRNA in tibia and lower IGF1 in bone and serum of SCD mice were partially restored after FMT from Ctrl feces. These data indicate that the healthy gut microbiota of Ctrl mice is protective for SCD bone loss through regulating IGF1 in response to impaired bacterial metabolites SCFAs.

Osteoporosis in children and young adults

Osteoporosis is a major public health problem with serious long-term complications. In children, the definition of osteoporosis is not only based on densitometric criteria but also takes into account vertebral and long bone fragility fractures. Several factors, such as long-term high-dose steroids, chronic inflammation, malnutrition, immobility, lack of sex steroids, and medication can reduce bone density and increase the risk for fragility fractures when left untreated. Also, genetic conditions can predispose to primary bone fragility disorders, with osteogenesis imperfecta being the most common. Furthermore, since the growing skeleton is at an increased rate of bone remodeling, the ability to heal long bone fractures and reshape vertebral fractures differentiates children from adults. The scope of this chapter is to review the risk factors of osteoporosis and fragility fractures and describe the commonest causes of primary and secondary osteoporosis and their management in children and young adults.

Myelopathy in sickle cell disease: a case-oriented review

INTRODUCTION

Although neurological complications are well recognized in patients with sickle cell disease, myelopathy has been rarely described, with few reported cases of compressive and ischemic myelopathy. We present the first case report of longitudinally extensive myelitis (LETM) in SCD and review the differential diagnosis of myelopathy in these patients.

CASE PRESENTATION

We report the case of a 29-year-old African-Brazilian man with SCD, who experienced a subacute flaccid paraparesis, with T2 sensory level and urinary retention. Cerebrospinal fluid analysis showed a lymphocytic pleocytosis and increased protein levels. MRI disclosed a longitudinally extensive spinal cord lesion, with a high T2/STIR signal extending from C2 to T12. We searched Medline/PubMed, Embase, Scopus, and Google Scholar databases for myelopathy in SCD patients.

DISCUSSION

Spinal cord compression by vertebral fractures, extramedullary hematopoietic tissue, and Salmonella epidural abscess have been reported in SCD. We found only three case reports of spinal cord infarction, which is unexpectedly infrequent compared to the prevalence of cerebral infarction in SCD. We found only one case report of varicella-zoster myelitis and no previous report of LETM in SCD patients. Specific and time-sensitive causes of myelopathy should be considered in SCD patients. In addition to compression and ischemia, LETM is a possible mechanism of spinal cord involvement in SCD patients.