Subcutaneous panniculitis-like T-cell lymphoma
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Synonyms and keywords: SPTCL; Subcutaneous panniculitis-like T-cell lymphoma alpha/beta subtype; Subcutaneous panniculitis-like T-cell lymphoma gamma/delta subtype; SPTCL-AB; SPTCL-GD

# Overview
Subcutaneous panniculitis-like T-cell lymphoma (SPTCL) is a rare type of T-cell non-Hodgkin lymphoma (NHL). Subcutaneous panniculitis-like T-cell lymphoma is a cytotoxic T-cell lymphoma, which preferentially infiltrates subcutaneous tissue, primarily involving the extremities and trunk. According to the World Health Organization-European Organization for Research and Treatment of Cancer, SPTCL is classified under Primary Cutaneous T-Cell Lymphomas and expresses the TCR phenotype (SPTCL-AB). TCR phenotypes are now a separate entity from SPTCL, known as the Cutaneous  T-cell Lymphoma. On microscopic histopathological analysis, atypical lymphoid cells, fat necrosis,and karyorrhexis are characteristic findings of subcutaneous panniculitis-like T-cell lymphoma. Depending on the extent of the tumor at the time of diagnosis, the prognosis may vary and the 5-year survival rate of patients with subcutaneous panniculitis-like T-cell lymphoma is approximately 80%. Symptoms of the SPTCL include fever, weight loss, night sweats, and painless swellings on extremities and trunk. Subcutaneous nodule biopsy is diagnostic of SPTCL. The predominant therapy for SPTCL is chemotherapy. Adjunctive radiotherapy and stem cell transplant may be required.

# Classification
Subcutaneous panniculitis-like T-cell lymphoma is classified under Primary cutaneous lymphomas and expresses the TCR phenotype.

# Pathophysiology
Subcutaneous panniculitis-like T-cell lymphoma is a cytotoxic T-cell lymphoma, which preferentially infiltrates subcutaneous tissue, primarily involving the extremities and trunk.

## Microscopic Pathology
On microscopic histopathological analysis, atypical lymphoid cells, fat necrosis, and karyorrhexis are characteristic findings of subcutaneous panniculitis-like T-cell lymphoma.

# Causes
There are no established causes for subcutaneous panniculitis-like T-cell lymphoma.

# Differentiating SPTCL from other Diseases
Subcutaneous panniculitis-like T-cell lymphoma must be differentiated from other diseases such as: 
- Benign panniculitis
- Extranodal NK-T-cell lymphoma
- Lupus erythematosus panniculitis
- Primary cutaneous CD56+ Natural Killer-like T-Cell lymphoma
- Primary cutaneous anaplastic large cell lymphoma
- Mycosis Fungoides
- Blastic plasmacytoid dendritic cell neoplasm
- Primary cutaneous lymphomas

# Differentiating Blastic NK cell Lymphoma from other Diseases
ABBREVIATIONS
N/A: Not available, NL: Normal, FISH: Fluorescence in situ hybridization, PCR: Polymerase chain reaction, LDH: Lactate dehydrogenase, PUD: Peptic ulcer disease, EPO: Erythropoietin, LFTs: Liver function tests, RFTs: Renal function tests, LAP: Leukocyte alkaline phosphatase, LAD: Leukocyte alkaline dehydrgenase, WBCs: White blood cells.

# Epidemiology and Demographics

## Age
Subcutaneous panniculitis-like T-cell lymphoma commonly affects young adults (35 years).

## Gender
Females are more commonly affected with subcutaneous panniculitis-like T-cell lymphoma than males.
The female to male ratio is 2:1.

# Risk Factors
There are no established risk factors for subcutaneous panniculitis-like T-cell lymphoma however, many patients have an associated autoimmune disorder at diagnosis.

# Screening
According to the the U.S. Preventive Service Task Force (USPSTF), there is insufficient evidence to recommend routine screening for subcutaneous panniculitis-like T-cell lymphoma. 

# Natural History, Complications and Prognosis
- Painless nodules form under the skin in the subcutaneous tissue (subcutaneous nodules).  
- Skin nodules may demonstrate regression with lipoatrophy at the site of the lesion.
- New nodules can appear at different sites over the course of the disease.
- The nodules commonly occur in the extremities or trunk. Other areas include: face, neck and back.
- Skin nodules range in size from 0.5 cm to several centimeters in diameter. Larger nodules may become necrotic, ulceration is rare.
- The infiltrate involves the fat lobules, usually sparing the septa. The overlying dermis and epidermis are typically uninvolved. Dissemination to lymph nodes and other organs is rare.
- People with this type of lymphoma can also develop a very serious condition where certain parts of the immune system are activated (hemophagocytic syndrome).
- Hemophagocytic syndrome causes:
- Fever
- Enlarged liver and spleen (hepatosplenomegaly)
- A lower number of red blood cells, white blood cells and platelets in the blood (pancytopenia)
- Failure to thrive
- Maculopapular rash
- CNS symptoms
- Lymphadenopathy
- Coagulopathy
- Abnormal LFTs
- High serum Ferritin
- Depending on the extent of the tumor at the time of diagnosis, the prognosis may vary and the 5-year survival rate of patients with subcutaneous panniculitis-like T-cell lymphoma is approximately 80%

# Diagnosis

## Symptoms
Symptoms of  SPTCL include: 
- Fever
- Chills
- Weight loss
- Night sweats
- Myalgias
- Painless swellings on extremities and trunk

## Physical Examination

### Vitals
- Fever is often present

### Skin
- Subcutaneous nodules
Abdomen
- Hepatosplenomegaly

## Laboratory Findings
Laboratory tests for subcutaneous panniculitis-like T-cell lymphoma include:
- Complete blood count (CBC): cytopenia
- Blood chemistry studies: Increased liver function tests
- Cytogenetic analysis
- Flow cytometry
- Immunophenotyping
- Positive: BetaF1; CD8; CD30; CLA; T-cell intracellular antigen (T1A1); and perforin
- Negative: CD3; CD5; and CD56

### Biopsy
Subcutaneous nodule biopsy is diagnostic of subcutaneous panniculitis-like T-cell lymphoma.

### Other Imaging Findings
CT, MRI, and PET scan may be helpful in the diagnosis of subcutaneous panniculitis-like T-cell lymphoma.

# Treatment

## Medical Therapy