What are the symptoms of Rocky Mountain spotted fever?

Rocky Mountain Spotted Fever: Clinical Symptoms

Rocky Mountain spotted fever presents initially with nonspecific symptoms of fever, headache, and malaise, with the characteristic rash appearing 2-4 days after fever onset in most patients—but critically, less than 50% have a rash in the first 3 days and up to 20% never develop a rash at all. 1

Early Symptoms (First 3 Days)

The initial presentation is typically nonspecific and includes:

• Fever (sudden onset, present in nearly all cases) 1, 2
• Headache (severe, one of the most common early symptoms) 1, 2
• Malaise and fatigue 1, 2
• Myalgias (muscle pain throughout the body) 1, 2
• Chills 1, 2
• Nausea and vomiting 1
• Abdominal pain (can mimic appendicitis, cholecystitis, or gastroenteritis) 1, 2
• Anorexia 1, 2
• Photophobia 1, 2

Rash Characteristics and Timing

The classic triad of fever, rash, and tick bite is present in only a minority of patients at initial presentation, so clinicians must not wait for this triad before initiating treatment. 1, 3

Rash Evolution:

• Initial appearance: Small (1-5 mm diameter) blanching pink macules on ankles, wrists, or forearms, typically appearing 2-4 days after fever onset 1, 2
• Progression: Spreads to palms, soles, arms, legs, and trunk over subsequent days, usually sparing the face 1
• Advanced stage: Becomes maculopapular with central petechiae 1
• Classic petechial rash: Appears by day 5-6, involving palms and soles, indicating advanced disease 1, 2

Critical Rash Pitfalls:

• Less than 50% of patients have rash in first 3 days of illness 1, 3
• Up to 20% of patients never develop a rash 3, 4
• Rash may be atypical, localized, faint, or difficult to recognize in darker-skinned individuals 1
• Children under 15 years develop rash more frequently and earlier than adults 1
• Absence or late-onset rash is associated with diagnostic delays and increased mortality 1

Additional Clinical Features

• Conjunctival suffusion 1
• Periorbital and peripheral edema (more common in children) 1
• Calf pain 1
• Hepatomegaly and splenomegaly 1
• Diarrhea 1, 2

Severe Late-Stage Manifestations (Untreated Disease)

If treatment is delayed beyond day 5-6, severe complications develop:

• Meningoencephalitis 1, 2
• Acute renal failure 1, 2
• Acute respiratory distress syndrome (ARDS) 1, 2
• Cutaneous necrosis and gangrene (particularly digits) 1, 2
• Shock 1, 2
• Cardiac arrhythmias 2
• Seizures 2
• Disseminated intravascular coagulation (DIC) (rare) 1

Laboratory Findings

Common laboratory abnormalities include:

• Thrombocytopenia 1
• Hyponatremia 1, 4
• Elevated hepatic transaminases (slight increase) 1
• Normal or slightly increased white blood cell count with increased immature neutrophils 1
• Elevated creatine kinase or lactate dehydrogenase (later in course) 1

Timing and Mortality Risk

• Incubation period: 3-12 days after tick bite 1, 2
• Shorter incubation (≤5 days) associated with more severe disease 2
• Case-fatality rate: 5-10% overall 1, 4
• 50% of deaths occur within 9 days of illness onset 3
• Mortality increases dramatically with treatment delay: Patients treated after day 5 have significantly higher mortality, with 33-50% mortality by days 6-9 if treatment is delayed 1

Critical Clinical Pearls

Only approximately 60% of patients recall tick exposure, so absence of tick bite history should not exclude the diagnosis. 3, 5 The disease occurs most commonly April through September in wooded, shrubby, or grassy areas. 5, 6 Delay in recognition and treatment is the single most important factor associated with death from RMSF. 1, 2