Differentials
Hirschsprung's disease
SIGNS / SYMPTOMS
Neonatal onset with failure to pass meconium within 24 hours, abdominal distension, vomiting, and subsequent failure to thrive.
INVESTIGATIONS
Rectal biopsy showing hypertrophic extrinsic nerve bundles and an absence of ganglion cells in the myenteric and submucosal plexus.
Anorectal manometry proves absence of a recto-anal inhibitory reflex.
Anorectal anomaly
SIGNS / SYMPTOMS
Position of the anus is ectopic or absent.
INVESTIGATIONS
Examination under anaesthetic and imaging shows degrees of ectopia, covered anus, rectovaginal fistula, or types of imperforate anus.
Group A streptococcal perianal skin infection
SIGNS / SYMPTOMS
Bright red erythema and local oedema.
INVESTIGATIONS
Growth of the organism from skin swab culture.
Anal fissure
SIGNS / SYMPTOMS
Generally associated with history of fresh blood on stool or nappy, and skin tag with very painful defecation. Characteristically in midline directly anterior or posterior.
INVESTIGATIONS
Diagnosis is based on clinical appearance.
Lichen sclerosus
SIGNS / SYMPTOMS
Thickened whitish perianal and vulval skin associated with deep fissures.
INVESTIGATIONS
Positive response to topical corticosteroids.
Anal sexual abuse
SIGNS / SYMPTOMS
Disclosure may be withheld but fissure may extend beyond anal margin and in lateral positions.
Depending on time from assault, there may be redness or bruising locally.
Reflex anal dilation may be seen but should not be confused with the reflex relaxation of the internal sphincter seen with a faecally impacted rectum.
INVESTIGATIONS
Expert multi-disciplinary disclosure interviews and forensic examination to seek semen or evidence of sexually transmitted diseases.
Myotonic dystrophy
SIGNS / SYMPTOMS
Dramatically gaping anus often in association with constipation. Evidence of myopathic facies, motor delays, cataract, or premature frontal balding. Presence of family history of myotonia.
INVESTIGATIONS
Genetic testing confirms the diagnosis.
Tethered spinal cord
SIGNS / SYMPTOMS
Low anal sphincter tone when rectum loaded, back pain, inability to bend trunk, and sometimes sacral or lumbar spine haemangioma, sinus tract, or skin defects.
INVESTIGATIONS
MRI scan of spine may show degrees of spinal dysraphism, thickening of cauda equina, lipoma, fatty filum cord tethering, or intraspinal tumour or syrinx.
Drug-induced
SIGNS / SYMPTOMS
Worsening of symptoms with starting medication, typically opioids.
INVESTIGATIONS
Discontinuation of medication.
Cows' milk intolerance
SIGNS / SYMPTOMS
Typically in infancy. Anus may appear reddened, and other signs of atopy (e.g., eczema) may be present.
INVESTIGATIONS
Infrequent positive skin tests or specific IgE tests. Resolution of constipation during exclusion diet.
Gluten enteropathy (Coeliac disease)
SIGNS / SYMPTOMS
Frequently associated with poor weight gain, abdominal pain, abdominal distension.
INVESTIGATIONS
Positive coeliac screening (i.e., anti-tissue transglutaminase IgA, anti-endomysial IgA) and atrophic duodenal mucosa on biopsy.
Crohn's disease
SIGNS / SYMPTOMS
Fleshy skin tags and local oedema with deep fissures often associated with abdominal pain, poor weight and growth, and oral lesions.
INVESTIGATIONS
Endoscopy, biopsy, radio-isotope scan. Findings suggestive of Crohn's disease include submucosal oedema, rigidity, pseudodiverticulae, or fistulisation. Deep ulcerations result in a cobblestone appearance.
Hypothyroidism
SIGNS / SYMPTOMS
Usually pan-colonic delayed transit constipation in association with poor height velocity and associated conditions such as diabetes mellitus in older children.
INVESTIGATIONS
Elevated thyroid-stimulating hormone (this is the most important in this age range).
Generally positive anti-thyroid antibodies, as neonatal hypothyroidism is detected by screening before the onset of constipation.
Neurofibromatosis
SIGNS / SYMPTOMS
Appearance of skin (i.e., café au lait spots).
Megarectum is a recognised complication.
INVESTIGATIONS
Fibromata may be seen on scans of the central nervous system.
Cystic fibrosis
Mitochondrial disease
SIGNS / SYMPTOMS
Multiple gastrointestinal complaints of poor movement including nausea, vomiting. Other systemic symptoms, fatigue, pain, cardiovascular abnormalities.
INVESTIGATIONS
Skin biopsy, which may show abnormalities consistent with mitochondrial disease including abnormal electron transport chain activity and beta-oxidation disorders.
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