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Corticosteroid Mechanism & Systemic Complications
Mechanism of Action
Corticosteroids remain the backbone of acute uveitis treatment because they act broadly across the inflammatory cascade rather than on a single cytokine or cell type. The core mechanism is induction of lipocortin-1 (annexin A1), which inhibits phospholipase A2. Phospholipase A2 is the enzyme that liberates arachidonic acid from cell membrane phospholipids, the first committed step toward both the cyclooxygenase (prostaglandin) and lipoxygenase (leukotriene) pathways. By blocking that step upstream, corticosteroids shut down production of both classes of inflammatory mediators at once, rather than inhibiting just one enzyme downstream the way an NSAID does. This upstream, broad-spectrum action is what makes corticosteroids fast and effective for acute inflammatory control. The same breadth underlies their long list of systemic side effects, since the pathways they suppress are not specific to ocular or even immune tissue.
The Corticosteroid-Sparing Threshold
Because of that broad systemic footprint, chronic maintenance dosing of systemic corticosteroids for uveitis is generally kept below roughly 7.5 mg of prednisone per day. Above this threshold, the risk of the complications covered below, including osteoporosis and cataracts, rises substantially with continued exposure. In practice, this threshold is the clinical trigger for adding a steroid-sparing immunosuppressive agent (an antimetabolite, calcineurin inhibitor, or biologic; see the related pages below) rather than simply continuing to taper corticosteroids and accept undertreated inflammation. The goal of steroid-sparing therapy is not to eliminate corticosteroids outright but to get the maintenance dose down to a level where long-term systemic risk is acceptable.
HPA Axis Suppression & Adrenal Insufficiency
Exogenous corticosteroids suppress the hypothalamic-pituitary-adrenal (HPA) axis by providing negative feedback that reduces endogenous corticotropin-releasing hormone and ACTH secretion. With sustained suppression, the adrenal cortex itself can atrophy from disuse. This matters most at the point of stopping therapy: abrupt discontinuation of long-term systemic corticosteroids can precipitate an adrenal (Addisonian) crisis, because the adrenal glands are left unable to produce adequate endogenous cortisol on their own, particularly during physiologic stress such as illness or surgery. This is why chronic steroid courses are always tapered rather than stopped abruptly.
The degree of HPA axis suppression, and therefore whether it's safe to taper further or stop, is assessed with the cosyntropin (synthetic ACTH) stimulation test. It measures the adrenal cortisol response to an exogenous ACTH challenge, helping determine whether the axis has recovered enough for steroids to be safely withdrawn.
Cushingoid Features
Chronic corticosteroid excess produces an iatrogenic Cushingoid appearance: moon facies, central or truncal obesity, and a dorsocervical fat pad ("buffalo hump"), driven by corticosteroid-induced redistribution of body fat toward the face, trunk, and upper back. It reverses gradually with dose reduction. Recognizing it clinically is useful both for counseling patients and for catching unrecognized long-term steroid exposure (topical, inhaled, or injected) in a patient who isn't known to be on treatment.
Musculoskeletal Complications
Osteoporosis
Corticosteroids decrease osteoblast activity while increasing osteoclast activity, producing rapid bone loss and elevated fracture risk, particularly at the spine and hips. This is one of the most common long-term complications of chronic steroid therapy and is a major part of the rationale for the sparing threshold above: bone density loss accrues with cumulative exposure and doesn't fully reverse just because the steroid is later stopped.
Avascular Necrosis
Corticosteroids can also cause avascular (aseptic) necrosis, most classically of the femoral head, through fat emboli formation and vascular compromise within bone. It presents with hip pain and reduced range of motion and, unlike osteoporosis, isn't reliably dose-related. It can occur even with relatively short high-dose courses, which makes it one of the more unpredictable steroid complications.
Myopathy
Steroid myopathy characteristically produces weakness in proximal limb muscles (difficulty rising from a chair or climbing stairs) because it preferentially affects type II (fast-twitch) muscle fibers. Creatine kinase is typically normal, which helps distinguish it from an inflammatory myopathy.
Metabolic, Psychiatric, and Other Systemic Effects
Hyperglycemia
Corticosteroids induce hepatic gluconeogenesis and peripheral insulin resistance, frequently causing new-onset hyperglycemia or worsening pre-existing diabetes, sometimes called "steroid diabetes." Glucose monitoring is warranted in any patient on a significant steroid course, diabetic or not.
Hypertension
Corticosteroids with mineralocorticoid activity promote renal sodium and water reabsorption, expanding intravascular volume and contributing to drug-induced hypertension.
Neuropsychiatric Effects
Corticosteroids can produce a spectrum of neuropsychiatric effects (euphoria, mania, agitation, and even frank psychosis), especially at higher doses, warranting dose monitoring and psychiatric assessment when symptoms emerge.
Growth Suppression in Children
In pediatric patients, chronic systemic corticosteroid therapy suppresses growth, affecting final adult height. Corticosteroids inhibit growth hormone secretion and directly impair growth plate chondrocyte function, making growth monitoring an essential part of managing pediatric uveitis that requires long-term steroids.
Gastrointestinal Risk with NSAIDs
Corticosteroids alone modestly increase peptic ulcer risk, but combined with NSAIDs the risk of gastrointestinal bleeding and ulceration rises substantially, due to synergistic mucosal injury. The combination is worth flagging when a patient on chronic steroids is also using NSAIDs for unrelated joint or muscle pain.
Which Complications Reverse, and Which Are Permanent
Most metabolic and functional effects improve once the dose falls. Structural damage generally does not, which is why the complications in the bottom rows carry the most weight when deciding to add a steroid-sparing agent early. Recovery also depends on dose, duration, and the patient.
| Complication | After dose reduction or stopping |
|---|---|
| Usually reversible | |
| Cushingoid fat redistribution | Resolves gradually over months; any skin striae may persist |
| Hyperglycemia | Usually improves; may persist if the steroid unmasked underlying diabetes |
| Hypertension | Usually improves |
| Neuropsychiatric effects | Usually resolve with dose reduction, often within days to weeks |
| Myopathy | Recovers slowly, over weeks to months |
| HPA axis suppression | Recovers gradually, and can take up to about a year after long courses; stress-dose cover may be needed meanwhile |
| Peptic ulcer risk | Risk falls once the steroid or NSAID is stopped; a bleed or perforation can still leave lasting harm |
| Partly reversible | |
| Osteoporosis | Bone density recovers only partly; established fractures are permanent |
| Growth suppression | Some catch-up growth is possible, but lost adult height can be permanent |
| Steroid-induced ocular hypertension | Pressure usually falls after stopping, but any glaucomatous optic nerve damage is permanent; see ocular complications |
| Permanent | |
| Avascular necrosis | Established necrosis does not recover, and may need joint replacement |
| Posterior subcapsular cataract | Does not regress meaningfully; treated with surgery if visually significant |
High-Yield Pearls
- Corticosteroids induce lipocortin-1, which inhibits phospholipase A2: one upstream step blocking both prostaglandin and leukotriene production at once.
- Chronic maintenance dosing above roughly 7.5 mg/day of prednisone is the clinical trigger for adding steroid-sparing immunosuppression.
- Usually reversible: Cushingoid change, hyperglycemia, hypertension, mood effects, myopathy, HPA suppression. Permanent: avascular necrosis, fractures, cataract, glaucomatous nerve damage.
- The cosyntropin stimulation test assesses HPA axis recovery before a chronic steroid course can be safely discontinued.
- Steroid myopathy hits proximal muscles with a normal creatine kinase, a useful distinguisher from inflammatory myopathies.
Never stop a chronic systemic corticosteroid course abruptly. Long-term use suppresses the HPA axis and can leave the adrenal glands unable to mount an adequate cortisol response. Abrupt discontinuation risks a genuine adrenal (Addisonian) crisis, not just a symptomatic flare of the underlying uveitis.
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